Developmental milestones and growth

• By 2 months most infants smile when spoken to and hold the head up on the tummy; by 12 months most pull to stand and use 1 to 2 words; by 24 months most walk alone and put 2 words together; by 5 years most speak in sentences, draw a person and play cooperatively.
• Developmental delay means slower acquisition of skills; a delay in one domain, or one missed milestone, is a reason for closer surveillance and screening, while missing milestones across domains, asymmetry, or any loss of skills is more concerning.
• Loss of a previously acquired skill is regression, not delay, and it always needs prompt evaluation because it can signal serious neurological, metabolic or epileptic disease.
• Growth is monitored with standardised charts; for children under 2 years the WHO standards are used, and from 2 years upward the CDC charts are used, plotting weight, length or height, head circumference in infants, and later BMI.
• When growth or development is a concern, the basics are the same everywhere: a careful history and examination, age-appropriate hearing testing, early referral for intervention services, and investigations guided by clinical findings.

By the end of this page you should be able to:

1. List the gross motor, fine motor, language and social milestones expected from 2 months to 5 years, and explain why milestone ages describe what most children (about three quarters) can do rather than the average.
2. Tell a developmental delay from regression, and list the red flags that should trigger screening and referral.
3. Plan the initial evaluation of a child with developmental delay, including the hearing check that is mandatory for language delay.
4. Recognise the early warning signs of autism spectrum disorder in the first 5 years.
5. Interpret a growth chart, define failure to thrive and the approach to short stature, and use mid-parental height and bone age in that assessment.
6. Describe normal and abnormal growth velocity and what catch-up growth is and when it is expected.

Developmental paediatrics is about watching children acquire skills across four linked domains: motor, language and communication, cognitive, and social-emotional. ^[1] Health supervision visits are the natural setting for this, and every visit is a chance to track progress, listen to parental concerns and act early. Surveillance is a longitudinal conversation and examination, not a single test; screening is the use of a validated tool at recommended ages or when surveillance raises concern; evaluation is the detailed diagnostic assessment that follows. ^[1] Milestones guide surveillance but they are not themselves validated tests, which is why a child who fails one should be screened, not simply reassured. ^[1]

Medical students should also remember that children are not small adults. Growth is continuous, especially in the first two years, and development proceeds along partly predictable tracks but with wide normal variation. The pillars of assessment are therefore a careful history, direct observation, accurate measurement plotted on the right chart, and the habit of asking "compared with the child's own previous measurements" rather than relying on a single number.

A milestone is a skill that most children can do by a given age. The CDC revised checklists apply the rule that a milestone is included only when about three quarters or more of children would be expected to reach it by that age. ^{[1] [2]} That is deliberately stricter than older lists, which often used median (50th percentile) ages and could be read as permission to wait. ^[1] Developmental warning signs were dropped from those lists for the same reason: not reaching a milestone that most children reach is itself the warning. ^[1]

The four classic domains are social-emotional, language and communication, cognitive (learning and problem-solving), and motor. Milestones are placed in the domain where families are most likely to observe them, even though the skills overlap. ^[1] Table 1 combines the milestones that define each age band; it is a teaching summary of what most children show, not a screening tool.

A concern list is more useful than a checklist of averages. Act early is the message: do not wait when a child is not meeting one or more milestones, has lost a skill, or when the family has concerns. ^[2] Referral routes include the primary care team, developmental paediatrics, neurology, audiology, and early intervention services. ^[5]

Red flags that should prompt screening, and usually referral, in the first five years include: ^{[2] [3] [4]}

• No social smile by 2 months, or no reciprocal facial expression by 3 to 4 months.
• No head control or asymmetric movements by 4 months; hand preference or using one side markedly more than the other before 12 months.
• No sitting without support by 9 months, or no crawling or transfer of objects by 9 to 10 months.
• No babbling by 12 months, or no use of gestures such as waving or pointing by 12 months.
• No single words by 16 to 18 months, even allowing for normal variation in first words.
• Still not combining two words by 24 months.
• No independent walking by 18 months.
• Not responding to the child's own name by 9 months.
• Any loss of language, social, motor or self-care skills at any age.
• Persistent primitive reflexes, unusual tone, or marked asymmetry on examination.
• Concerning social-communication features such as poor eye contact, lack of shared interest, or repetitive behaviours (see the autism section).

When to refer urgently: any regression, new asymmetry, a head that is growing too fast or too slowly, seizures, or focal neurological signs should be referred the same day or within days. Earlier-but-less-urgent referral is appropriate when a child is more than about two developmental age bands behind, is not progressing on repeated assessment, or has red flags listed under autism or growth.

Eligibility for formal developmental screening between recommended ages should be judged clinically: the purpose is to decide whether a validated screening tool is needed, not to replace evaluation. ^[1]

Delay and regression are not the same and the words should not be used interchangeably. Delay means a skill is acquired later than expected; the child is on the same path but moving more slowly. Regression means a skill that was present is lost. Regression is never normal: it suggests an active process affecting the nervous system or hearing, and it demands timely assessment for epilepsy, neurodegenerative or metabolic disease, acquired brain injury, or autistic regression. ^{[2] [3]}

Delay may be isolated to one domain (speech delay in an otherwise social child with normal hearing) or global (delay across motor, language and social domains). Global delay prompts a broader search for cause, including genetics, prenatal exposures, perinatal events, chronic illness and nutrition. ^[5] The distinction matters for families too: delay often improves with therapy and early intervention, whereas regression needs explanation of cause and monitoring.

Every child with delayed language needs hearing tested as soon as the delay is recognised; do not wait for a milestone birthday before referring. Hearing loss can be subtle and behaviour alone does not detect it: a child may appear to hear some sounds and not others, turn to a voice seen but not called from behind, or turn the television volume up. ^[4] Early hearing screening is universal in many systems (all babies screened by 1 month), and any baby who does not pass should have a full diagnostic audiology assessment by about 3 months. ^[4] Children should also be tested whenever there is concern, including before school entry. ^[4]

Practical points:

• Ask about newborn hearing screening results and risk factors such as neonatal intensive care, meningitis, jaundice requiring exchange transfusion, craniofacial abnormalities, or a family history of childhood hearing loss. ^[4]
• Re-test hearing if language stalls or regresses, or if there is recurrent otitis media.
• If hearing is normal, distinguish receptive from expressive language delay; reduced understanding is more worrying than isolated late talking.
• Refer to speech and language therapy and early intervention; treat the child, not just the test result.
• Remember that social communication delay with otherwise intact articulation points away from hearing loss and toward autism spectrum disorder.

Autism spectrum disorder presents with differences in social communication and interaction and with restricted or repetitive patterns of behaviour and interest. ^[3] The signs are developmental, so they overlap with milestones: not pointing to share interest by 15 to 18 months, not responding to the name by 9 months, limited eye contact, and few or no gestures by 12 months are common early clues. ^[3] Communication and social milestones that are not met deserve attention even when motor milestones are normal. ^[3]

Warning signs by age include: ^[3]

• By 6 to 9 months: avoiding or not keeping eye contact; no warm facial expressions by 9 months; not responding to name by 9 months; not playing interactive games such as pat-a-cake by 12 months.
• By 12 to 15 months: few or no gestures; not pointing or waving by 12 months; not sharing interests by 15 months.
• By 18 to 24 months: not pointing to show something interesting by 18 months; not noticing others' feelings by 24 months. ^[3]
• By 3 to 5 years: not joining other children in play by 3 years; no pretend play by 4 years; not singing, dancing or acting by 5 years.

Restricted and repetitive features include lining up toys, repeating words or phrases (echolalia), playing with toys the same way each time, intense focus on parts of objects, distress at minor changes, hand flapping or body rocking, and unusual reactions to sound, smell, taste, sight or texture. ^[3] Not every child with autism shows all of these, and none of them should be used as a label from a single observation; but together they are the reason to refer. ^[3] Loss of speech, babbling, or social skills at any age is a particular red flag for autism and for neurological disease and should be acted on immediately. ^{[2] [3]}

Growth is assessed by plotting accurate measurements on standardised charts. ^{[8] [9]} Growth charts are percentile curves showing the distribution of body measurements in children; they contribute to the picture but are not a sole diagnostic instrument. ^[8] In routine practice the WHO growth standards are used from birth to 2 years and the CDC growth charts from 2 years upward, although the WHO standards themselves run to 5 years (60 completed months). ^{[8] [9]} Measure recumbent length until 2 years and standing height thereafter, weight, head circumference in infants and toddlers, and BMI from 2 years. ^{[8] [5]}

The percentile matters less than the trend. A healthy child may ride any centile from the 3rd to the 97th; concern arises when a child falls away from the centile they have been following, crosses downward through two or more centile spaces, or sits below about the 2nd centile without an obvious family explanation. ^[5] Growth velocity is what the chart shows over time; single measurements can be misleading, especially in infants. ^[5]

Faltering growth means growth that is not following the expected pattern, most often reflecting inadequate nutrition relative to need. Thresholds for concern include: ^[5]

• A fall across 1 or more weight centile spaces if birth weight was below the 9th centile. ^[5]
• A fall across 2 or more weight centile spaces if birth weight was between the 9th and 91st centiles. ^[5]
• A fall across 3 or more weight centile spaces if birth weight was above the 91st centile. ^[5]
• Current weight below the 2nd centile for age, whatever the birth weight. ^[5]

Excessive early weight loss after birth (more than 10% of birth weight, or failure to regain birth weight by 3 weeks) also warrants assessment and feeding support. ^[5]

Measurement and assessment: weigh and measure length (under 2 years) or height (over 2 years), plot with prior measurements, calculate BMI from 2 years upward (BMI below the 2nd centile may reflect undernutrition or a small build; below the 0.4th centile probable undernutrition), and take a detailed feeding history and clinical, developmental and social history. ^[5] Investigations beyond urine and, where gluten-containing foods have been introduced, coeliac disease are usually unhelpful in a well child with no other concerns. ^[5] Refer when there are signs of systemic illness, rapid weight loss or severe undernutrition, slow linear growth or unexplained short stature, failure to respond to primary care interventions, or safeguarding concerns. ^[5]

Short stature means height below about the 2nd or 3rd centile for age. ^[7] Evaluation has two aims: identify any disease or endocrine problem, and judge whether the height fits the family and genetic potential. The steps are: accurate standing height measured with a stadiometer and plotted on the sex- and age-appropriate chart; accurate weights; assessment of growth velocity and of body proportions; examination for dysmorphism, chronic disease, and pubertal stage; parental heights for mid-parental height; bone age radiograph; and targeted laboratory or genetic investigations guided by history, examination and growth pattern. ^{[5] [7]}

Red flags that point away from a benign familial picture: height falling well below the level predicted from parental heights; growth velocity clearly reduced for age; disproportion (short trunk or short limbs); dysmorphic features; chronic symptoms (gastrointestinal, respiratory, renal); severe or rapid deceleration; and a child much shorter than predicted by parental heights. ^{[5] [7]} If the child's length or height centile is more than 2 centile spaces below the mid-parental centile, consider undernutrition or a primary growth disorder. ^[5]

The target height (mid-parental height) estimate most widely used is the Tanner formula, which takes the average of the parents' heights and corrects for the sex difference of about 13 cm: ^[6]

• Target height (boys) = (father's height + [mother's height + 13 cm]) / 2
• Target height (girls) = ([father's height - 13 cm] + mother's height) / 2

This calculated target height carries a normal range of about ± 8.5 cm, reflecting within-family variation. ^[6] It is a guide, not a fate: tall/short parents tend to have less extreme children through regression to the mean, the parent sex difference varies between populations (about 13.2 cm in UK data, 13.3 cm on the WHO charts), secular trends have made newer generations taller in many countries, and the formula tends to underestimate the growth potential of children with very short parents. ^[6] Always measure parents rather than rely on reported heights when possible.

Bone age assessment compares a radiograph of the hand and wrist (most often the left) with standard atlas images, conventionally the Greulich-Pyle or Tanner-Whitehouse methods. ^[7] It estimates skeletal maturity and is a standard part of evaluating short stature, pubertal timing, and predicted adult height. A bone age matching chronological age supports constitutional delay or normal variation; a significantly delayed bone age raises the possibility of hormone deficiency or chronic illness; an advanced bone age raises the possibility of early puberty or other pathology. ^[7] Skeletal maturation typically precedes that of boys by about 2 years in girls. ^[7] Automated methods are now available, but clinical interpretation still benefits from awareness of their limitations and from consistent expert review. ^[7]

Growth velocity is not constant: it is highest in infancy, slower and steadier in childhood, and rises again at puberty. ^{[8] [9]} Abnormal velocity is suspected when a child's measurements drift downward across centiles, when annual height gain is clearly below what would be expected for that age band, or when the height SDS falls steadily away from the mid-parental target. Always interpret velocity in context: prematurity, chronic disease, nutritional intake, medications such as corticosteroids, and psychosocial factors. In low-resource settings even a single tape-measured height with a simple chart can detect the child whose measurements flatten out over months.

Growth is usually re-measured no more often than needed; for children with faltering growth the guide is length or height no more often than every 3 months. ^[5] More frequent weighing can increase parental anxiety without improving care. ^[5]

Catch-up growth is the accelerated growth that occurs after a period of growth suppression (malnutrition, chronic illness, prematurity, or an endocrine problem) once the underlying cause is corrected. It tends to bring the child's height and weight back toward the genetic centile, and it is most complete when the insult was short in duration and occurred early. Some children, particularly those born small for gestational age, show continued catch-up into mid-childhood. The opposite, catch-down growth, brings an oversized infant (often after maternal diabetes or high birth weight) back toward their genetic centile over a variable period. Over-interpretation of short periods of acceleration or deceleration should be avoided, as measurement error and illness can mimic true change.

Refer when: a child has regressed; has red flags for autism; is failing milestones across domains; has clear asymmetry or tone abnormality; has significant growth concerns or unexplained short stature; has not responded to early intervention; or when the family's concerns persist after normal screening. Early referral usually improves outcome because intervention services act on the delay, not the label.

• Use whatever standard chart is available and plot accurately; even a simple weight-for-age chart identifies growth failure.
• Measure length/height with a board or tape and consistent technique; record in the parent-held record.
• Refer to the local early intervention or rehabilitation service for motor delay; for speech delay, check hearing first using affordable screening methods.
• Most children with delayed milestones will not receive a diagnosis, but almost all can receive help; focus on function and participation.

• A milestone is a skill most children (about three quarters) can do by a given age, not the average age.
• Surveillance, screening and diagnostic evaluation are three separate steps.
• Red flags include no babbling by 12 months, no words by 16 to 18 months, still no word pairs at 24 months, no independent walking by 18 months, poor response to name by 9 months, and any loss of skills at any age.
• Regression is abnormal and urgent; delay is slower acquisition and may be isolated or global.
• Every language delay needs a hearing assessment.
• Autism warning signs overlap with milestone failure, especially in social communication and shared interest.
• Use WHO growth standards under 2 years and CDC charts from 2 years upward; track weight, length or height, head circumference in infants, and BMI thereafter.
• Failure to thrive is assessed by centile trend and defined thresholds; refer for systemic features, severe undernutrition, rapid loss, or poor response.
• Short stature assessment combines height, velocity, body proportions, family heights (mid-parental target with about 13 cm sex correction), and bone age.
• The Tanner target height has a range of about ± 8.5 cm and underestimates growth potential in very short parents. ^[6]
• Bone age is assessed from a hand and wrist radiograph with standard atlas methods.
• Catch-up growth follows correction of the underlying cause and is most complete when brief and early.

Developmental delay and growth should be read alongside topics on prematurity and small-for-gestational-age infants, infant feeding, nutrition, autism spectrum disorder, hearing loss, genetic short stature, thyroid disorders in children, and cerebral palsy. These related topics are listed here as plain text pending verified links.