What a milestone list actually is

The CDC revised its developmental milestone checklists in February 2022, and the revision changed what a listed age means. Milestones are now placed "at ages by which at least 75% of children would be expected to exhibit them, in an effort to make even one missing milestone more 'actionable' (likely to prompt screening and possible referral)." The CDC explains the reasoning: "with a milestone at 50%, half of all children would still reasonably be expected to have not yet achieved it. This change is intended to reduce the 'wait and see' approach."

The CDC is equally careful about the limits. Its checklists "are not developmental guidelines or standards for children's development. They should not be used as screening or diagnostic tools to detect developmental delays", and "if developmental concerns are noted, the next steps are screening and evaluation with formal tools or referral for services." It also notes the lists "do not contain all possible milestones children might exhibit."

The HSE says the same in plainer language on every milestone page: "the ages given for milestones in this guide are an average. Every child is different."

The flag that outranks all the others

Loss of previously acquired skills is a referral flag at any age. This deserves stating without qualification because it is the one thing that is not a range.

The CDC includes it in the standard instruction on every checklist: "if your child is not meeting one or more milestones, has lost skills he or she once had, or you have other concerns, act early." It is also one of the five questions it asks parents to raise with a doctor: "has your child lost any skills he/she once had?"

The HSE repeats "loses skills they had before" as a reason to contact a GP or public health nurse at 14 months, 16 months, 20 months, 24 months, 3 years, 4 years and 5 years — every single age band it publishes, without exception. A child who used to wave and no longer does, who had a dozen words and now has three, or who used to walk and has stopped, needs to be seen. Not watched. Seen.

The other red flags, by age

The HSE publishes explicit "contact your GP or public health nurse" lists, which is more useful than a generic milestone table.

Around 14 months: does not say words that have meaning; does not point to objects; does not give much eye contact; shows little interest in other people.
Around 16 months: is not standing independently; is not walking with support.
Around 20 months: is not walking independently; cannot speak at least 6 words.
Around 3 years: cannot walk up and down stairs independently; cannot run or jump; cannot communicate their needs; cannot follow straightforward commands.
Around 4 to 5 years: cannot walk, run, climb, jump or use stairs confidently; cannot catch, throw or kick a ball; cannot communicate their needs.

Two items on that list carry more weight than their wording suggests. No pointing appears at 14 months, and the CDC lists "points to show you something interesting" among its 18-month milestones. Pointing to share, rather than to demand, is one of the earliest signs of social communication, and its absence is worth raising on its own. Cannot communicate their needs appears at every age from three onwards, and is deliberately broader than "cannot talk" — a child who gets their meaning across by gesture is communicating.

What else is worth raising

The NHS's description of autism in young children is a useful checklist for things that are easy to normalise. Autistic children may "start to speak at a later age than other children", "not respond to their name", "not speak much or use single words", "repeat words and phrases", "use eye contact less often", "use fewer facial expressions and gestures", "not seem interested in other children", "find it hard to join in playing with other children", "not take part in pretend play", enjoy repetitive actions, do repetitive movements such as rocking or hand flapping, and "be worried or upset by changes in routine".

The NHS also flags sensory differences that families often put down to fussiness: reacting very strongly or not at all to lights, sounds, smells, tastes or textures; only eating certain foods or eating in a particular way; and disliking certain clothes or materials. It notes signs can be harder to see in girls, who "may be more likely to copy how other children behave and play" and "appear to cope with social situations".

Hearing sits underneath most concerns about speech and social response and is easy to check. If your child is not responding to their name or their speech is not progressing, ask directly whether their hearing has been tested recently.

How the UK system is meant to catch this

The NHS offers a health and development review at 2 to 2.5 years, usually with a health visitor or nursery nurse, at home, at a clinic or at your child's nursery or childminder. It covers "general development, including movement, speech, social skills and behaviour, and hearing and vision", growth and eating, managing behaviour and sleep, teeth, safety and vaccinations.

You will be sent an Ages and Stages Questionnaire (ASQ-3) beforehand. The NHS's advice is not to worry if you cannot complete it all — "a health visitor will help you complete it." The red book (personal child health record) is the place to keep this and anything else you want raised, and the NHS suggests keeping the developmental milestones section up to date yourself.

One correction that matters for premature children: "if your baby was born prematurely, their developmental age will be calculated from your original due date, not from the actual date they were born, until they are 2 years old." A baby born ten weeks early should be assessed against their corrected age, and the CDC asks parents to tell the doctor if a child was born prematurely for the same reason.

Critically, none of this means waiting. The NHS says: "if you have any concerns at other times, you can contact a health visitor or GP, or go to your local baby clinic."

Concerns are common, and that is the point

The Royal College of Paediatrics and Child Health's State of Child Health data gives some scale. In Scotland, where developmental concerns are recorded at routine reviews, "in 2024-25, 14% of children who received a 13-15-month review, 17% of those at 27-30-month review, and 19% of those at 4-5-year review had at least one developmental concern recorded." In England, 68.3% of children achieved a Good Level of Development at age 5 in 2024, against a government ambition of 75% by 2028.

The RCPCH also notes why acting early is worth the effort, and why it can be slow: "long waiting lists for children's community health services, such as in speech and language therapy ... can result in delays in diagnosing and mitigating any developmental delays." A referral made now is a place in a queue that only gets longer if you wait to be certain.

How to raise it, and what to say

The CDC's five questions are the best script for the appointment: what do you and your child do together; what does your child like to do; is there anything your child does or does not do that concerns you; has your child lost any skills they once had; and does your child have any special healthcare needs or were they born prematurely.

If you are still concerned after that conversation, the CDC's next steps are to "ask for a referral to a specialist who can evaluate your child more" and to contact early intervention services. In the UK, the equivalents are your health visitor, GP, and your local speech and language therapy service — and the NHS is explicit that "if you prefer, you can refer your child to a speech and language therapist yourself." Nursery is an ally too: you can also speak to a special educational needs coordinator (SENCo) at your child's nursery.

The instruction the CDC repeats on every page is the right one to end on: "you know your child best. Don't wait."

When to Worry About Development