Developmental surveillance — the ongoing process of recognizing children who may be at risk for developmental delays — should occur at every well-child visit. Screening with standardized tools is performed at 9, 18, 24, and 30 months using validated instruments such as the Ages and Stages Questionnaire (ASQ) and the Modified Checklist for Autism in Toddlers, Revised (M-CHAT-R/F).
Milestones by Age
2 months. Social/emotional: begins to smile at people, briefly calms self. Language/communication: coos, turns head toward sounds. Cognitive: pays attention to faces, follows things with eyes. Motor: holds head up, pushes up on arms when on tummy.
4 months. Social/emotional: smiles spontaneously, laughs, enjoys play. Language: babbles with expression, copies sounds. Cognitive: reaches for objects, puts things in mouth. Motor: rolls front to back, sits with support, pushes up to elbows.
6 months. Social/emotional: knows familiar faces, enjoys looking at self in mirror, responds to others emotions. Language: takes turns making sounds, responds to name. Cognitive: brings things to mouth, closes to get a desired toy. Motor: rolls both ways, sits without support, rocks on hands and knees.
9 months. Social/emotional: shy with strangers, has favorite toys, understands no. Language: babbles mama/dada nonspecifically, points to things. Cognitive: watches the path of something falling, looks for hidden objects, bangs things together. Motor: stands holding on, crawls, pulls to stand, pincer grasp.
12 months. Social/emotional: plays games like pat-a-cake, waves goodbye, shows fear. Language: says mama/dada specifically, tries to copy words. Cognitive: explores things in different ways, finds hidden objects. Motor: walks with support, stands alone, takes a few steps.
15 months. Social/emotional: imitates activities, offers toys to others. Language: says 1–2 words, follows simple commands. Cognitive: uses objects correctly, points to ask for something. Motor: walks independently, stoops to pick up objects.
18 months. Social/emotional: plays pretend, points to show interest, parallel play. Language: says 10+ words, points to body parts. Cognitive: knows what common objects do, scribbles. Motor: runs, walks up stairs with help, drinks from a cup.
24 months (2 years). Social/emotional: copies others, shows defiance, plays alongside others. Language: says 50+ words, two-word phrases, follows two-step commands. Cognitive: builds towers of 4+ blocks, sorts shapes and colors. Motor: jumps, kicks a ball, climbs onto furniture.
30 months. Social/emotional: engages in cooperative play, shows a range of emotions. Language: says 200+ words, three-word sentences. Cognitive: completes simple puzzles. Motor: stands on tiptoes, throws overhand.
36 months (3 years). Social/emotional: shows affection, separates easily from parents, engages in imaginative play. Language: 200+ words, carries on dialogue, understands most of what is said. Cognitive: draws a circle, operates mechanical toys. Motor: pedals a tricycle, balances briefly on one foot.
48 months (4 years). Social/emotional: enjoys new things, pretends to be a parent. Language: tells stories, sings songs, says first and last name. Cognitive: draws a person with 2–4 body parts, counts 1–5. Motor: hops on one foot, catches a bounced ball.
60 months (5 years). Social/emotional: wants to please friends, likes to sing/dance/act, distinguishes real from pretend. Language: speaks clearly, tells a simple story, uses future tense. Cognitive: counts 10+ things, draws a person with 6+ body parts. Motor: stands on one foot for 10 seconds, skips, uses a fork and spoon.
Autism Spectrum Disorder Screening
The AAP recommends ASD screening at 18 and 24 months using the M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised, with Follow-Up). A positive screen warrants comprehensive diagnostic evaluation. Early signs: reduced eye contact, delayed babbling or pointing, lack of response to name, reduced social smiling, unusual sensory responses, repetitive movements (hand flapping, rocking), and insistence on sameness. Early intervention improves communication, social skills, and adaptive functioning.
Referral Pathways
Children identified with developmental concerns are referred to early intervention (birth–3 years, via state EI programs) or the local school district (3–5 years) for evaluation. Early intervention provides speech therapy, occupational therapy, physical therapy, developmental therapy, and family training. For children with suspected ASD, referral to a developmental-behavioral pediatrician, child neurologist, or autism specialty center for comprehensive evaluation.
Summary
Developmental surveillance with standardized screening at recommended ages identifies children at risk for developmental delays. Early identification and referral to early intervention services optimize outcomes. The CDC milestone checklists provide age-specific guideposts. Loss of previously acquired skills is an urgent red flag. Autism screening at 18 and 24 months is standard of care.