Wondering if your child is delayed? Milestones and developmental charts - Here is what you need to know.

Has this ever happened to you?

You watch your child intensely practicing a new movement.

The struggle, the concentration, the determined grunts and muffled noises of effort.

Nearly...Nearly...Almost...

But not quite.

They don't manage to stay in tummy time.

They don't roll.

They don't push up.

They don't take that long-awaited first step.

And somewhere in the back of your mind, a voice starts whispering:

They should have done this a month ago.

My friend's baby rolled at three months.

That baby on Instagram walked at eleven months.

Is something wrong? Is it something I did? Is it something I didn't do?

Am I somehow responsible for this?

And then - worst case scenario - your pediatrician at the next check-up peers over their glasses and confirms it. "Your child is a little behind the curve."

Cue: the full existential collapse.

Because it doesn't feel like a data point - it feels like a verdict and judgement. On you.

So let's talk about this - where milestones came from, what they actually mean, and why your child's perfectly individual timeline is not a report card on your parenting.

The Man Who Invented "Normal"

Developmental milestones as a formal concept are a surprisingly recent invention. 

We talk about them as though they are ancient wisdom carved into stone tablets, handed down through generations of wise elders who watched babies roll over and nodded knowingly.

They are not.

The whole framework was essentially built by one man, in one clinic, filming babies with a movie camera.

His name was Arnold Gesell.

A psychologist and pediatrician, he directed the Clinic of Child Development at Yale University from 1911 to 1948, where he did something nobody had done systematically before: he pointed a motion-picture camera at children, watched the footage back in obsessive detail, and built the first formal map of when things typically happen.

The Gesell Developmental Schedule was published in 1925 - and that checklist, compiled from a small and fairly homogeneous group of children in New Haven, Connecticut, is the direct ancestor of the chart your pediatrician is consulting today. Encyclopedia BritannicaNAEYC

Gesell was genuinely brilliant. He was also working with what he had, which was not a globally representative sample of human children. Critics noted that by stressing "normal stages of development," he seemed not to value a child's individuality. 

The norms were always meant to be a general map. They were never meant to function as a deadline.

And yet. Here we are.

Maria Montessori Had Something to Say About This

Around the same time Gesell was filming babies at Yale, a doctor named Maria Montessori was observing children in Rome and coming to a different conclusion - not when children do things, but why they are so driven to do them at all.

Montessori identified what she called "sensitive periods": windows of time during which a child's brain is primed and hungry for specific kinds of input.

The most important sensitive periods occur between birth and age six, and in other pedagogies they are commonly referred to as windows of opportunity or developmental milestones. Montessori Academy

Through her observations, Montessori proposed that children respond best to the introduction and practice of certain skills at different times in their development, identifying 6 main categories of sensitive periods, including movement, language, sensorial exploration, order, small objects, social interactions.

For the Sensitive Period of Movement, for  example: it lasts about 4 years, but between birth and 2.5 years old, children are especially interested in learning to coordinate and control their movements - gross and fine motor skills developing from touching and grasping to turning, crawling, balancing, walking and climbing. Maria Montessori discovered that children are particularly interested in walking between 12 and 15 months. The Montessori Site

Read that range again. Twelve to fifteen months. A three-month window. And that was coming from the woman who spent her entire career watching children with extraordinary precision.

The point both Gesell and Montessori were actually making is that development follows a sequence and a blueprint our children are born with and not a clock.

By giving them exposure and freedom to grow and develop their language, movement, senses - we are laying foundations for their natural development.

What the Research Actually Says About "Normal"

Here is the part that should make every parent exhale.

The World Health Organisation tracked when children around the world took their first independent steps and found that anywhere between 8 and 18 months is completely, unremarkably typical. That is a ten-month window for one milestone. Declared normal by the most authoritative health body on the planet.

So if your child is thirteen months old and still cruising the furniture while you quietly catastrophise into your coffee, you are well inside the bounds of ordinary.

A child with a quieter disposition may be less inclined to verbally communicate but possess perfectly normal receptive language skills.

Conversely, a sociable but risk-averse child might prefer to hold off on walking and focus more energy on communicating verbally with parents and caregivers.

Using strictly developmental milestone standards, this child might be flagged for a motor delay simply because they were more disposed to talking than exploring their environment. Nordic Naturals

Your child is not a machine running software updates on schedule. They are a human being with a temperament, a personality, and a set of priorities entirely their own.

Sometimes they are busy working on something else.

What This Looked Like in My House (Across Three Very Different Humans)

I have three children. I have therefore run this particular experiment three times, and I can report that the results were completely inconsistent and entirely instructive.

My first set the bar high. She hit every milestone at the textbook moment, like a tiny, cooperative research participant who had read Gesell's schedule in the womb and decided to oblige. She was the child that made me think I understood this.

I did not understand this.

My second was a master of psychological warfare. He would excel spectacularly - crawling at five months, which led me to announce to anyone who would listen that we had some kind of infant prodigy on our hands - and then grind to a complete halt. Lather, rinse, repeat. The ecstasy of "he is so advanced!" was followed, reliably, by the anxiety of "he will never walk."

He took his first independent steps at fifteen months. He is fine.

My third is a mystery wrapped in a very cheerful enigma. I took him to his one-year check-up, proud as anything, and the pediatrician looked up and said, with a slight tilt of the head: "He seems a bit slow."

The dragon within me woke up very suddenly.

But because it was my third child and I had at least some battle-hardened wisdom by then, I asked the follow-up question instead of combusting on the spot.

"Is this something we should be concerned about?"

She smiled and said: "Oh no. We see this a lot with third children."

Which brings me to the thing I wish someone had told me before child one: always, always ask the follow-up question.

"Behind the curve" is not a sentence. It's the beginning of a conversation.

And also: never compare.

Never do what mum Chilli does in that Bluey episode when she turns her baby daughter's developmental timeline into a competitive sport. The baby ignores the entire enterprise, naturally, and reaches her milestone on exactly the day she feels like it.

Children have been doing this since the beginning. They tend to arrive, eventually, where they are going.

What You Can Actually Control (And What You Cannot)

You cannot will your child to walk before their nervous system is ready.

You cannot download vocabulary into a brain that hasn't finished building the infrastructure for it.

You are not responsible for the timing - but you are the environment.

What Montessori understood and what the research backs up, is that your job is to provide the conditions, not to manufacture the outcome.

Recognising and supporting sensitive periods begins with observing your child and allowing them to progress at their own pace, providing a supportive learning environment that offers stimulus appropriate to their stage of development - including ensuring adequate time and materials - and respecting the individual interests and passions of your child. Montessori Academy

Tummy time. Floor time. Talking to them constantly, even when you feel like a lunatic narrating your own grocery unpacking. Books. Objects to reach for, spaces to move through, people to watch. Sensory classes, outdoor walks, interactions with other babies, children and adults. That is your job. The rest is theirs.

The blueprint is already inside them. They are, to borrow Montessori's framing, hardwired for mastery.

You are not building the house from scratch. You are making sure the conditions are right for it to rise.

So the next time you catch yourself spiraling over a missed milestone date on a chart that was designed over a century ago from a sample size that would not pass a modern ethics review - take a breath, ask your pediatrician the follow-up question, and go back to watching your child with curiosity instead of a stopwatch.

They know what they are doing. They are just doing it on their own terms.

Which, if you think about it, is exactly the kind of person you are trying to raise.

Read more about the Sensitive Period of Language - how if you miss it, your child might struggle to speak later: HERE

Watch the Bluey Episode Baby Race:

https://www.youtube.com/watch?v=xmkCmJtK6X8

Children aged 0-3years are absolute sensorial learners - they absorb knowledge about the world through all their senses - and you can help guide them on their quest by regularly joining sensory activities (through repetition they consolidate information and transform it into knowledge). Sign up for a series of Sensory for Babies classes (if your baby is 3-12m) or Sensory for Toddlers classes (walking kids up to 3y - with parent).

I cannot wait to see you learning alongside your child, together with us!

References

Gesell, A. (1925). The Gesell Developmental Schedule. Yale Clinic of Child Development.

Gesell, A., & Ilg, F.L. (1943). Infant and Child in the Culture of Today. Harper & Brothers.

Montessori, M. (1949). The Absorbent Mind. Clio Press.

Montessori, M. (1966). The Secret of Childhood. Fides Publishers.

Liu, W.Y., et al. (2017). Treadmill training with body weight support: Its effect on walkers with cerebral palsy. Gait & Posture, 54. [as cited in: Physio-pedia, Early Development of Toddler Walking]

World Health Organization Multicentre Growth Reference Study Group. (2006). WHO Motor Development Study: Windows of achievement for six gross motor development milestones. Acta Paediatrica Supplement, 450, 86–95.

Nordic Naturals Health Sciences. (2022). Understanding your child's developmental milestones. nordic.com

The Montessori Site. (2022). The 11 Montessori Sensitive Periods. themontessorisite.com