Developmental leaps

Developmental milestones by age, and what a delay really means

Milestones describe what most children do by a given age, not what every child must do by then. Wide variation is normal. Two things are worth acting on rather than watching: missing several milestones in one area, and losing a skill a child previously had.

Published 7 August 2026 · 9 min read

Milestone lists are the most anxiety-producing thing on the internet for new parents, mostly because of how they are written. A list that says “at 12 months, walks” reads like a deadline. It is not one.

What a milestone actually is

A milestone is a skill that most children can do by a given age. Public health bodies generally set them at the point where around three quarters of children have the skill — so by definition, a substantial minority of entirely typical children have not got there yet.

That framing changes what the list is for. It is not a test your child passes or fails. It is a prompt: if several are missing in the same area, that is worth mentioning to someone.

The four areas development is tracked in

Movement and physical. Rolling, sitting, crawling, walking; later, holding a pencil and using stairs.
Language and communication. Babbling, first words, following instructions, putting words together — set out age by age in the speech milestones.
Social and emotional. Smiling, responding to their name, showing you things, playing alongside other children.
Cognitive. Looking for a hidden object, using objects for their purpose, pretend play, solving simple problems.

The grouping matters more than any individual item. A child can be late walking and early talking; energy tends to go into one area at a time.

Milestones by age

A condensed view. Health bodies publish fuller checklists — the CDC’s is linked in the sources and is the one to use if you want the complete version.

Every one of these windows is months wide, and they overlap: a baby can be pulling to stand before another has rolled, and both be entirely typical. Walking anywhere from eleven to eighteen months needs no explanation.

Age	Movement	Communication	Social and thinking
2 months	Holds head up briefly	Makes sounds other than crying	Smiles at you, looks at your face
4 months	Pushes up on elbows, holds a toy	Coos, makes sounds back to you	Chuckles, looks at their hands
6 months	Rolls, sits with support	Takes turns making sounds	Recognises familiar people
9 months	Sits unsupported, gets to sitting	Babbles strings of sounds	Looks when you call their name
12 months	Pulls to stand, walks holding on	Waves, says a word or two	Plays give-and-take games
18 months	Walks alone, climbs on furniture	Several words, points to show you	Copies chores, plays pretend
2 years	Runs, kicks a ball	Two-word phrases, points to things in a book	Notices other children
3 years	Uses stairs one foot per step	Conversation of two or three exchanges	Plays alongside other children

Why the ranges are so wide

Normal variation is genuinely large, and several ordinary things move the timing:

Temperament. A cautious child may walk months after a reckless one and be identical in every other respect.
Opportunity. Skills need practice; a baby who is carried most of the day gets less floor time.
Focus. Progress in one area often pauses while another is being acquired.
Bilingual households. Children learning two languages sometimes reach single-language word counts a little later and are not delayed — total vocabulary across both languages is the fairer measure.

Corrected age for premature babies

For roughly the first two years, a premature baby’s development is measured from the due date rather than the birth date. A baby born eight weeks early is assessed as a ten-month-old at twelve months.

Getting this wrong is a common and unnecessary source of worry. If your baby was premature, do the correction before comparing against any list, including the one above.

What is worth acting on

The distinction that matters is a single late item versus a pattern.

Usually just timing

One milestone late while everything else is on time
Walking at 16 months in a child who communicates well
A quiet child in a family of quiet children who understands everything said to them

Worth raising

Several milestones missing in the same area
No new skills over a period of months
Not responding to their name by around 12 months
No pointing or gesturing by 18 months
No two-word phrases by around 2 years
Persistent difficulty with sounds, hearing or vision
A strong asymmetry — consistently using one side of the body much more before 18 months

Losing a skill is different

This deserves its own heading because it is the one thing on this page that should not be watched and waited on.

A child who used to say words and has stopped, who used to wave and no longer does, who used to make eye contact and now avoids it — that is a regression rather than a delay, and it should be raised with a doctor promptly. It is uncommon, it is usually explainable, and it is specifically the pattern worth acting on quickly.

Why acting early matters

The advice to raise concerns rather than wait is not about catastrophe. It is that the same support does more when it starts earlier, during the period when the brain is most adaptable.

Two things worth knowing:

You do not need a diagnosis to ask. A concern is enough to start an assessment.
Being wrong costs nothing. An assessment that finds no problem is a good outcome, not a wasted appointment.

Parents are also, statistically, quite good at this. A persistent feeling that something is different is worth voicing even when you cannot point at a specific missing item.

When to ask

Speak to your paediatrician, health visitor or GP if several milestones in one area are missing, if your child loses a skill they had, if you have concerns about hearing or vision, or if you simply have a persistent sense that something is different. You do not need to wait for the next scheduled review, and you do not need to be sure.

Questions parents ask

What are developmental milestones?

Skills that most children can do by a certain age — rolling, sitting, first words, pointing, pretend play. They are grouped into movement, language and communication, social and emotional, and thinking skills. They describe what is typical, not a standard every child must meet.

When should a baby start walking?

Most children walk somewhere between 9 and 18 months, and the whole of that range is normal. Walking later than average, on its own, in a child who is otherwise developing well, is usually just their timing.

When should I worry about a developmental delay?

When several milestones in the same area are missed rather than one, when there is no progress over months, or at any point if you have a persistent feeling that something is different. Raise it rather than waiting for the next check-up — assessment is free and reassurance is a good outcome.

What does it mean if my child loses a skill?

Losing a skill they previously had — words they used to say, waving they used to do, eye contact they used to make — is different from being slow to gain one, and it should be raised with a doctor promptly rather than watched.

Do premature babies hit milestones later?

They are usually assessed on corrected age — age from the due date rather than the birth date — for roughly the first two years. A baby born two months early is measured against a ten-month-old at twelve months.

Does missing a milestone mean something is wrong?

Usually not. Plenty of children reach one skill late and everything else on time, and catch up without any intervention. What changes the picture is a pattern across an area rather than a single item.

Sources

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