Parents are usually the first to notice that something about their child's development looks different. Sometimes the worry turns out to be variation within the normal range — children acquire skills at very different rates and the average is just an average. But sometimes the worry is genuine and acting on it early changes the long-term outcome. This article is the list of signs that should prompt a health visitor or GP appointment, not because something is necessarily wrong but because assessment at this age is low-cost and has a high payoff. For more on tracking development, visit Healthbooq.
The One Red Flag That Trumps Everything: Loss of Skills
If your child loses a skill they previously had — a baby who was babbling stops babbling, a toddler who had words loses them, a child who used to make eye contact starts avoiding it, a child who was walking starts crawling again — that needs prompt assessment regardless of age, regardless of how gradual it looks, and regardless of how many other things still seem fine. Skill regression is not a normal part of development. Even if it seems to partly recover on its own, it warrants a full review.
This is the one rule from this article worth memorising as a parent, because it overrides everything else.
Birth to 6 Months
By 2 months, the social smile typically appears — a real smile in response to a face or voice, not a wind smile. Concerns to raise:
- No social smile by 2 months
- Limited or absent eye contact at any age
- Not orienting to faces or voices
- Not following a moving object with their eyes by 3 months
- A baby who feels unusually floppy (low tone) or unusually stiff (high tone)
- Persistent fisting of one or both hands beyond 3 months
- Not bringing hands to midline by 4 months
By 5–6 months most babies are reaching for objects with both hands and bringing them to the mouth. Lack of any reach or interest in objects is a flag.
6 to 12 Months
This is the period where social engagement and pre-language behaviours come online and become observable. Things to flag:
- Not babbling (consonant-vowel combinations like "ba", "ma", "da") by 9–10 months
- Not responding consistently to their own name by 10 months
- No pointing or waving by 12 months
- No reaching out to be picked up
- Absent joint attention — not following your gaze when you look at something, not looking back at you when something interesting happens
- Not sitting with support by 9 months, or independently by 10 months
- Strong asymmetry — only using one side of the body, only one hand reaching, dragging one leg
Pointing at 12 months is one of the more sensitive early markers — the gesture that says "look at that, with me" is a building block for language and is a particular focus in autism screening (NICE quality standards on autism).
12 to 24 Months
Walking and first words land in this window. The key thresholds:
- Not walking independently by 18 months (the WHO 99th centile)
- No first single word by 16 months
- No two-word combinations (like "more milk", "Daddy go") by 24 months
- No pretend play by 18 months — not feeding a doll, not putting a toy phone to ear
- Not following a simple one-step instruction ("give me the ball") by 18 months
- Loss of any words they previously had (regression — see above)
- Notably limited understanding of language even if some words are produced
- Hand dominance established before 18 months — true handedness before 18 months can mean reduced function on the opposite side, sometimes from a perinatal stroke
Strong fixed routines that cause significant distress when disrupted, lack of interest in other children, very repetitive play with the same toy in the same way, and absent or unusual eye contact are also worth raising in this window — these are not diagnoses but they belong in the conversation.
24 to 36 Months
By 2 to 3 years, a child should have a vocabulary of at least 50 words and be combining them into short sentences. By 3, around half of what they say should be intelligible to people outside the family. Red flags:
- No two-word phrases by 24 months
- Vocabulary under 50 words at 24 months
- Speech that is largely unintelligible to unfamiliar adults by 30 months
- No use of pronouns (I, you, me) by 30–36 months
- Persistent echolalia (repeating speech rather than using language flexibly)
- Repetitive motor mannerisms (hand flapping, spinning, rocking) that are intense or interfere with daily activity
- Strong inflexibility around routine that produces extreme distress with small changes
- Highly restricted interests that exclude other engagement
- Unusual quality of social interaction — not seeking shared attention, limited reciprocity in play
These last several features are part of the autism profile and warrant a referral for assessment. NICE CG128 supports clinician referral for autism assessment when concerns are raised.
Hearing and Vision Are the Easy Wins
Before any developmental delay is investigated further, hearing and vision should be checked. Roughly 1 in 1,000 newborns has significant hearing loss, and newborn hearing screening catches most but not all. A child whose receptive or expressive language is behind needs an audiology assessment, full stop — much language delay is hearing loss until proven otherwise.
The same applies for any child not making good eye contact or not visually tracking — orthoptic and ophthalmology assessment first, then any further developmental work.
What to Do If You're Worried
In the UK, raise the concern with your health visitor — they can do a development review and refer onward. Don't wait for the next scheduled review if the concern is significant; ask for an earlier appointment. Your GP can refer to community paediatrics or directly to speech and language therapy. NHS speech and language services in many areas accept self-referral.
In the US, your pediatrician can refer to Early Intervention (state programs for under-3s) — these are generally free or low-cost and you do not need a diagnosis to access them. The principle is the same: act on concerns rather than waiting them out.
What you should not accept: being told "boys are slower," "wait and see," or "Einstein didn't talk till he was three" without an actual assessment. These reassurances may be true in any individual case but they are not a substitute for evaluation. Early intervention works — across speech, motor, and behavioural domains, the under-3 window is when the brain is most responsive to support.
What Assessment Actually Involves
The first step is usually a development review with a health visitor or pediatrician using a standardised tool (Ages & Stages Questionnaire, Schedule of Growing Skills, M-CHAT for autism screening). If anything looks atypical, referral follows — to speech and language therapy, physiotherapy, occupational therapy, audiology, ophthalmology, or community paediatrics depending on the concern. None of this commits a child to a diagnosis. It commits them to being looked at properly.
Many children referred for developmental concerns are eventually reassured. Some receive support services that help them catch up. A smaller group receive a diagnosis that opens up specific intervention. All three outcomes are better than waiting.
A Note on Parental Instinct
The research on parental concerns and developmental outcomes is consistent: when parents raise specific concerns about their child's development, those concerns are right more often than not. If your gut says something is different, the right move is an appointment, not reassurance from a relative. The system is set up to catch what you're seeing — but only if you tell it.
Key Takeaways
Developmental red flags are signs that warrant assessment, not diagnoses. The most important red flag at any age is loss of skills a child previously had. Other key thresholds: no social smile by 2 months, no babbling by 12 months, no first words by 16 months, no two-word phrases by 24 months, not walking by 18 months. Early intervention reliably improves outcomes — if a milestone has clearly been missed, ask for assessment rather than waiting it out.
