Glossary
Clear, research-based explanations of the baby development and health terms you’ll come across, written by Yuppo Lab Experts.
A
Active sleep (REM sleep)
The lighter stage of infant sleep in which the baby twitches, makes noises, breathes irregularly and moves their eyes under closed lids; newborns spend about half of their sleep in it.
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Allergen introduction
Offering foods that commonly cause allergies, such as egg and peanut, early in the complementary feeding period, one new food at a time so that any reaction can be traced to its source.
Learn moreAtopic dermatitis (eczema)
A long-lasting skin condition with dry, itchy, red patches that flare and settle, which in babies often starts on the cheeks and in the creases of the arms and legs.
Learn moreAttachment
The deep emotional bond a baby forms with the people who care for them consistently and responsively, first described in the work of John Bowlby.
Learn moreAutism spectrum disorder
A developmental condition defined by differences in social communication and interaction together with repetitive behaviours and restricted interests, with signs that often appear in the first two years.
Learn moreB
Babbling
Repeated consonant-vowel syllables such as "ba-ba" and "da-da", which usually appear between 6 and 9 months and lay the groundwork for first words.
Learn moreBabinski reflex
A newborn reflex in which the big toe lifts and the other toes fan out when the sole of the foot is stroked, usually disappearing between 1 and 2 years of age.
Learn moreBaby acne
Small red or white spots on a baby's face in the first weeks of life, which are harmless and usually clear without treatment.
Learn moreBaby blues
Tearfulness, mood swings and worry that many new mothers feel in the first days after birth, which usually pass on their own within two weeks.
Learn moreBaby bouncer
A low, reclined seat with a soft frame that rocks or bounces gently as the baby moves; it is meant for supervised awake time and not for sleep.
Learn moreBaby sling
A length of fabric worn across the parent's body to carry a baby close, which is safest when the baby's face is visible, their chin is off their chest and they sit high and snug.
Learn moreBaby walker
A wheeled frame a baby sits in and pushes with their feet, which the American Academy of Pediatrics advises against because of the risk of falls and injuries.
Learn moreBaby-led weaning (BLW)
A way of starting solids in which the baby feeds themselves soft, hand-held pieces of food instead of being spoon-fed purées, usually from around 6 months.
Learn moreBed-sharing
A baby sleeping in the same bed as a parent, which the American Academy of Pediatrics does not recommend because it raises the risk of sleep-related deaths.
Learn moreBedtime routine
A short series of calm activities, such as a bath, pyjamas, a book and a lullaby, repeated in the same order each evening to help the baby wind down for sleep.
Learn moreBilingual development
A child learning two or more languages from early childhood, which does not cause language delay.
Learn moreBiting
Young children biting others out of excitement, frustration or not yet having the words to express themselves, most common between 1 and 3 years.
Learn moreBreastfeeding
Feeding a baby with breast milk, which the World Health Organization recommends exclusively for the first 6 months and alongside solid foods up to 2 years and beyond.
Learn moreBronchiolitis
A viral infection of the small airways of the lungs that is common in children under 2 and is most often caused by RSV.
Learn moreBurping
Holding a baby upright and gently patting or rubbing their back to release air swallowed during feeding.
Learn moreC
Catnap
A short daytime nap, often lasting less than a single sleep cycle of about 30-45 minutes, after which the baby wakes and struggles to settle back to sleep.
Learn moreChewing skills
The ability to break down and mash food in the mouth before swallowing, which starts with the gums before teeth appear and develops as the baby meets new textures.
Learn moreChild-led play
Play in which the adult follows the child's interests and ideas rather than directing the activity.
Learn moreCircadian rhythm
The body's roughly 24-hour internal clock that regulates sleep, hormones and body temperature, which in babies starts to develop around 2-3 months of age.
Learn moreCluster feeding
A baby wanting to feed very frequently over a few hours, often in the evening, which is common in the early weeks.
Learn moreCo-regulation
The process by which a calm adult helps a baby settle strong feelings through their voice, touch and presence, before the child can regulate emotions on their own.
Learn moreCognitive development
The development of thinking, learning, memory and problem-solving skills.
Learn moreColic
Long periods of intense, inconsolable crying in a healthy baby with no clear cause, classically defined as more than 3 hours a day, on more than 3 days a week, for at least 3 weeks.
Learn moreColostrum
The thick, yellowish first milk produced in the first days after birth, which comes in small amounts but is rich in antibodies and other protective factors.
Learn moreComplementary feeding
Introducing solid foods alongside breast milk or formula, which the World Health Organization recommends starting at around 6 months.
Learn moreCooing
The first soft vowel sounds other than crying, such as "aaa" and "ooo", which usually begin around 2 months.
Learn moreCooperative play
Children playing together towards a shared goal with agreed rules or roles, which usually develops in the preschool years.
Learn moreCorrected age
For a baby born early, their actual age minus the number of weeks they were born early, used to follow their development until about 2 years of age.
Learn moreCortisol
A hormone released by the adrenal glands that helps the body respond to stress and regulates energy; in babies its daily pattern of being higher in the morning develops in the first months.
Learn moreCradle cap
Yellowish, greasy, scaly patches on a baby's scalp (seborrheic dermatitis), which are harmless and usually clear on their own.
Learn moreCrawling
Moving forward on hands and knees or on the tummy, which many babies start between 6 and 10 months, although some skip it altogether.
Learn moreCruising
Taking sideways steps while holding on to furniture, which usually begins between 9 and 12 months and comes before walking independently.
Learn moreD
Dehydration
The body loses more fluid than it takes in, which can develop quickly in babies with diarrhoea, vomiting or fever.
Learn moreDevelopmental dysplasia of the hip (DDH)
A condition in which the hip joint does not form normally, checked at newborn examinations and with ultrasound when needed.
Learn moreDevelopmental leap
A popular term for periods when a baby is temporarily more unsettled, feeds more often or sleeps worse, believed to coincide with developmental changes.
Learn moreDevelopmental milestone
A skill that most children reach by a certain age, such as smiling, sitting or walking; in the CDC's 2022 checklists, each milestone is a skill at least 75% of children show by that age.
Learn moreDevelopmental regression
The loss of a skill a child had already gained, such as words or social skills, which should always be discussed with a doctor.
Learn moreDevelopmental screening
A short assessment using standard tools to identify developmental delays early, which the American Academy of Pediatrics recommends at 9, 18 and 30 months.
Learn moreDiaper rash
Red, irritated skin in the diaper area caused by moisture and friction, which usually improves with frequent changes, air drying and a barrier cream.
Learn moreDidactic play
Play with materials designed to teach a specific skill or concept, such as shape sorters, puzzles or stacking rings, where there is usually one correct way to use them.
Learn moreE
Ear infection (otitis media)
An infection of the middle ear that often follows a cold and can cause fussiness, fever, poor sleep and ear pulling.
Learn moreEarly intervention
Support services such as physical, speech and occupational therapy for babies and toddlers who have, or are at risk of, developmental delays.
Learn moreEarly rising
A baby regularly starting the day much earlier than expected, for example before 5 am, often linked to morning light, bedtime or nap timing.
Learn moreEmotional regulation
The ability to recognise, manage and recover from strong feelings, which develops gradually throughout early childhood with the support of caregivers.
Learn moreExpressive language
The ability to communicate thoughts and needs through sounds, gestures, words and sentences.
Learn moreF
Febrile seizure
A fever-induced seizure in children aged 6 months to 5 years. Although typically brief with no long-term harm, every first-time episode requires professional medical assessment, and any prolonged, repeated, or focal seizure warrants urgent emergency intervention.
Learn moreFever
A body temperature of 38°C (100.4°F) or higher, which in babies under 3 months always needs prompt medical assessment.
Learn moreFine motor skills
Movements that use the small muscles of the hands and fingers, such as grasping, passing objects between hands and picking up small items.
Learn moreFontanelle
The soft spots between the bones of a baby's skull, the larger front one of which usually closes between 12 and 18 months.
Learn moreFourth trimester
A term for roughly the first 12 weeks after birth, when the baby adjusts to life outside the womb and the family adjusts to a new rhythm.
Learn moreG
Gag reflex
A protective reflex that pushes food that is too large or too far back towards the front of the mouth, which is normal when a baby starts solids.
Learn moreGas pain
Discomfort caused by air trapped in a baby's digestive system, often blamed for fussiness, although most gas in babies is normal and harmless.
Learn moreGestures
Body movements a baby uses to communicate before speaking, such as waving, raising their arms to be picked up or shaking their head for "no", most of which appear between 9 and 12 months.
Learn moreGross motor skills
Movements that use the large muscles of the body, such as holding up the head, rolling, sitting, crawling and walking.
Learn moreGrowth chart
A chart used to track a child's length, weight and head circumference over time and compare them with children of the same age and sex.
Learn moreGrowth spurt
A short period, usually a few days, when a baby grows rapidly and seems hungrier, wanting to feed more often.
Learn moreGuided play
Play that the child leads while an adult gently steers it towards a learning goal, for example by setting up materials, asking questions or offering hints.
Learn moreH
Head control
A baby's ability to hold their head steady without it wobbling, which strengthens with tummy time and is usually well established by 4 months.
Learn moreHiccups
Short, involuntary contractions of the diaphragm that are very common and usually harmless in newborns.
Learn moreI
Imitation
A baby copying other people's facial expressions, sounds and actions, one of the most basic ways babies learn.
Learn moreInfant botulism
A rare but serious illness in babies under 12 months caused by Clostridium botulinum bacteria growing in the gut, which is why honey should never be given to babies under 1 year.
Learn moreInfant formula
A manufactured milk designed to meet a baby's nutritional needs, used instead of or alongside breast milk.
Learn moreIron supplementation
Giving iron drops to babies whose natural birth iron stores begin to deplete (typically around 4 to 6 months), preterm infants, or those with identified deficiency, under medical guidance.
Learn moreJ
Joint attention
A baby and an adult focusing on the same object or event together and sharing that interest, usually established between 9 and 12 months and a cornerstone of language development.
Learn moreK
Kangaroo care
Prolonged, regular skin-to-skin contact between a parent and baby, used especially for preterm and low-birth-weight babies.
Learn moreL
Language acquisition
The process by which a child learns to understand and use language, from cooing and babbling to a first word around 12 months and then to sentences.
Learn moreLanugo
Fine, soft hair that covers a baby's body in the womb, often still visible at birth in preterm babies and shed in the first weeks.
Learn moreLate talker (speech delay)
A toddler whose spoken language is behind that of peers, commonly defined as using fewer than about 50 words or not combining words by age 2.
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Mastitis
An inflammation of breast tissue most commonly occurring during lactation characterized by localized breast pain, redness, swelling, and systemic flu-like symptoms such as fever and chills.
Learn moreMeconium
A newborn's first stool, which is dark green-black and sticky and is usually passed within the first 24-48 hours.
Learn moreMelatonin
A hormone released mainly in darkness that tells the body it is night, which babies begin producing in a regular daily rhythm at around 2-3 months.
Learn moreMoro reflex
A startle reflex in which a baby flings their arms out and then pulls them in after a loud sound or a sense of falling, usually disappearing by 4-6 months.
Learn moreN
Nap
A short period of sleep a baby takes during the day, with the number of naps decreasing as the child grows.
Learn moreNap transition
A period when a child drops a daytime nap, for example moving from two naps to one, often with temporary fussiness and a need for an earlier bedtime.
Learn moreNewborn blood spot screening (heel prick)
A test in which a few drops of blood from a newborn's heel are used to screen for rare but treatable conditions such as phenylketonuria and congenital hypothyroidism.
Learn moreNewborn hearing screening
A quick, painless test done in the first days or weeks of life to detect hearing loss early.
Learn moreNewborn jaundice
Yellowing of a newborn's skin and the whites of the eyes caused by a build-up of bilirubin, which is common in the first week.
Learn moreNewborn screening
The set of tests offered to all babies shortly after birth, usually including the heel prick blood test, a hearing test and in many countries a pulse oximetry check for heart defects, to find treatable conditions early.
Learn moreNight terrors
Episodes of partial waking from deep sleep in which a child screams and seems awake but is actually still asleep, most common in the preschool years.
Learn moreO
Object permanence
The understanding that objects and people still exist when they are out of sight, described by Jean Piaget and usually emerging between 6 and 9 months.
Learn moreOpen-ended play
Play with materials that have no single correct use, such as blocks, boxes or fabric, which puts the child's imagination first.
Learn moreOral thrush
A yeast infection that causes white patches on a baby's tongue and inner cheeks that do not wipe off easily, and that can also affect a breastfeeding parent's nipples.
Learn moreOverstimulation
A baby becoming unsettled after too much noise, light, activity or interaction, often shown by turning away, avoiding eye contact or crying.
Learn moreOvertiredness
A state in which a baby has been awake too long and becomes harder to settle, often sleeping less well as a result.
Learn moreP
Pacifier
A soft nipple-shaped object that satisfies a baby's need to suck; the American Academy of Pediatrics notes that offering one at sleep time may lower the risk of SIDS.
Learn moreParallel play
Children playing side by side with similar toys without directly interacting, most noticeable between 2 and 3 years.
Learn moreParental burnout
Physical and emotional exhaustion that develops when the demands of parenting outweigh a parent's resources for a long time, often with emotional distance from the child and a sense of failure.
Learn moreParentese
The slower, higher-pitched, sing-song way adults naturally speak to babies, using real words, which research shows supports language development.
Learn morePercentile
A number on a growth chart showing how a child's measurement compares with children of the same age and sex, so that the 30th percentile means larger than 30% of them.
Learn morePeriod of PURPLE Crying
A name for the normal phase in the first months of life when crying increases, peaking around 2 months and easing by 3-5 months.
Learn morePicky eating
A child accepting only a limited range of foods and refusing new ones, most common between 2 and 6 years.
Learn morePincer grasp
Picking up small objects between the tips of the thumb and index finger, which usually develops between 9 and 12 months.
Learn morePointing
Using the index finger to ask for something or to share interest with someone, which usually appears between 12 and 15 months.
Learn morePositional plagiocephaly (flat head)
Flattening of part of a baby's head caused by lying in the same position for long periods.
Learn morePostpartum depression
Persistent sadness, loss of interest, hopelessness or anxiety lasting more than two weeks in the months after birth, which can affect both mothers and fathers and is treatable.
Learn morePretend play
Play in which a child acts out situations or uses an object as if it were something else, such as holding a block to the ear like a phone, usually emerging between 18 months and 2 years.
Learn morePrimitive reflexes
Automatic movements babies are born with, such as rooting, sucking, grasping and the Moro reflex, most of which fade as the brain matures.
Learn morePulling to stand
A baby pulling themselves up to standing by holding on to furniture or a person, which usually happens between 8 and 10 months.
Learn moreQ
Quiet sleep (non-REM sleep)
The deeper stage of infant sleep in which the baby lies still and breathes slowly and regularly.
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Receptive language
The ability to understand words, sentences and gestures, which in babies develops ahead of the ability to speak.
Learn moreReflux (spit-up)
Milk coming back up from the stomach into the food pipe and mouth, which is very common in babies and usually improves within the first year.
Learn moreResponsive caregiving
Noticing a baby's signals and responding to them promptly and appropriately, one of the five components of the World Health Organization's Nurturing Care Framework.
Learn moreResponsive feeding
Feeding a baby in response to their hunger and fullness cues rather than by the clock or a set amount.
Learn moreRolling over
A baby turning from tummy to back or back to tummy on their own, which usually happens between 4 and 6 months.
Learn moreRoom-sharing
A baby sleeping in the parents' room on a separate sleep surface, which the American Academy of Pediatrics recommends ideally for at least the first 6 months.
Learn moreRSV (respiratory syncytial virus)
A common respiratory virus that most children catch by age 2, which usually causes cold-like symptoms but can lead to bronchiolitis in young babies.
Learn moreS
Safe sleep
Sleep practices that lower the risk of SIDS and sleep-related accidents, including placing the baby on their back for every sleep on a firm, flat surface with no soft items in the cot.
Learn moreScreen time
Time a child spends looking at screens, which the World Health Organization does not recommend for children under 2.
Learn moreSensory play
Play that engages the senses using materials such as water, sand, dough and different textures.
Learn moreSensory processing
The way the brain receives, organises and responds to information from the senses, such as touch, sound, light and movement.
Learn moreSensory sensitivity
A stronger than usual reaction to sensory input such as loud sounds, bright lights, certain textures or clothing labels.
Learn moreSeparation anxiety
A baby crying and clinging when separated from the people they are attached to, usually emerging between 8 and 10 months and a normal sign of attachment.
Learn moreServe and return
Back-and-forth exchanges in which a baby sends a signal and an adult responds with a look, words or touch, which Harvard's Center on the Developing Child describes as essential for building brain architecture.
Learn moreSetting limits
Showing a child the boundaries of safe and acceptable behaviour in a calm, clear and consistent way.
Learn moreShaken baby syndrome (abusive head trauma)
Serious brain injury caused by violently shaking a baby, which can lead to blindness, seizures, lasting disability or death.
Learn moreSitting
A baby sitting upright, first with support and then without, with independent sitting usually achieved by 9 months.
Learn moreSkin-to-skin contact
Placing a baby, wearing only a diaper, directly on a parent's bare chest, which helps regulate the baby's temperature and breathing and supports breastfeeding.
Learn moreSleep association
Something a baby links with falling asleep, such as feeding, rocking or a pacifier, which they may then need in order to fall back asleep.
Learn moreSleep cycle
A repeating sequence of active and quiet sleep that lasts about 40-60 minutes in babies, with brief waking between cycles being normal.
Learn moreSleep regression
A popular term for a period when a baby who was sleeping well temporarily starts sleeping worse.
Learn moreSleep training
An umbrella term for methods that help a baby learn to fall asleep on their own, which most experts do not suggest before 4-6 months.
Learn moreSleeping through the night
A baby sleeping for a long stretch at night without waking, often defined in research as 6-8 hours of unbroken sleep.
Learn moreSleepy cues
Signs that a baby is getting tired, such as yawning, rubbing their eyes, staring into space or becoming fussy.
Learn moreSnoring
Noisy breathing during sleep caused by partly blocked upper airways, which is often temporary during a cold but should be checked by a doctor if it happens regularly.
Learn moreSocial referencing
A baby looking at a parent's face to decide how to react in an unfamiliar situation, usually seen from around 9-12 months.
Learn moreSocial smile
A smile a baby gives on purpose in response to a face or voice, which usually first appears around 2 months.
Learn moreSocial-emotional development
A child's growing ability to form relationships, understand and express emotions, and manage their feelings and behaviour.
Learn moreSoothing
Ways of calming a crying or unsettled baby, such as holding, rocking, shushing, a pacifier or skin-to-skin contact.
Learn moreStranger anxiety
A baby becoming wary or upset around unfamiliar people, which often appears around 8-9 months and is a normal stage of development.
Learn moreSudden Infant Death Syndrome (SIDS)
The sudden, unexplained death of a seemingly healthy baby under 1 year, usually during sleep, with the highest risk in the first 6 months.
Learn moreSwaddling
Wrapping a baby snugly in a thin blanket with the hips free to move, which should stop once the baby shows signs of trying to roll.
Learn moreSymbolic play
Play in which a child uses an object, action or word to stand for something else, such as using a banana as a phone, an early sign of abstract thinking.
Learn moreT
Tantrum
An outburst in which a young child expresses intense feelings by crying, shouting or throwing themselves down, most common between 1 and 3 years.
Learn moreTeething
The process of baby teeth breaking through the gums, with the first tooth usually appearing around 6 months.
Learn moreTelegraphic speech
Early sentences of two or three key words without small grammatical words, such as "mummy come" or "give ball", which usually appear around age 2.
Learn moreTemperament
A baby's inborn way of responding to the world, including activity level, adaptability and intensity of emotions.
Learn moreToilet training
Learning to use a potty or toilet instead of diapers, which most children are ready for between 2 and 3 years.
Learn moreTongue-tie (ankyloglossia)
A condition in which the strip of tissue under the tongue is short or tight and restricts the tongue's movement, sometimes making feeding harder.
Learn moreTorticollis
A condition in which tight neck muscles cause a baby to tilt their head to one side and turn their chin to the other.
Learn moreTransitional object
A blanket, soft toy or similar item a child becomes attached to and uses for comfort, especially during separations and at bedtime.
Learn moreTummy time
Placing a baby on their tummy while awake and supervised to strengthen the neck, shoulder and back muscles.
Learn moreU
Umbilical cord
The cord that connects the baby to the placenta in the womb, whose remaining stump should be kept clean and dry after birth until it falls off, usually within 1-3 weeks.
Learn moreV
Vaccination
Giving vaccines to protect against serious infectious diseases, according to a schedule set by each country's health authority.
Learn moreVernix caseosa
The white, cheese-like coating that protects a baby's skin in the womb, any remainder of which is absorbed naturally after birth.
Learn moreVitamin D supplementation
Giving vitamin D drops to babies to support healthy bones, especially breastfed babies, as breast milk usually contains little vitamin D.
Learn moreVocabulary spurt
A period when the number of words a child uses increases rapidly, often starting around 18 months.
Learn moreW
Wake window
A popular term for the length of time a baby can comfortably stay awake between sleeps, which gets longer with age.
Learn moreWalking
Taking steps independently without support, which some babies start at 9-10 months and others closer to 18 months.
Learn moreWhite noise
A steady, constant background sound, such as a fan or shushing, that helps some babies fall asleep and stay asleep.
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