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In the beginning, everything is everything

Charts split child development into four areas because that’s convenient. A young baby doesn’t. How movement, language, thinking and feeling travel together at first, and slowly become distinct.

What are the areas of child development?

Most milestone charts use four: physical (or motor), cognitive, linguistic, and social–emotional. The categories are useful. But in Chapter 2 of Big Bang Baby I argue that in the earliest months, sharp lines between them say more about how adults organize things than about how a baby grows. It is one child, seen from four sides.

What does the research show?

This idea is where the book, and its title, began. Working with Michael Frank and his team at Stanford, we saw that a young baby who is a little ahead in one area tends to be a little ahead in the others too. Early on, the four areas rise and fall almost as one. Around the first birthday, that link loosens.

In 2026 we repeated the analysis on Kinedu’s records at a much larger scale, following the same children over time. The coupling between areas fell from 0.489 to 0.265 across the first year, nearly half, and stayed lower through 35 months without reaching zero. These are Kinedu data, from an internal analysis of roughly 3.5 million children that has not yet been published with peer review. It used the same assessment as the Stanford work, so it confirms the pattern rather than testing it independently.

In Chapter 2 I describe the end of that curve this way: “The four domains do not become four strangers.”

How do motor skills affect language?

Follow what one physical skill makes possible. A baby who has just gained steady control of her head can turn toward your voice, keep your face in view long enough to study it, and glance between you and the toy you’re holding. A motor milestone is also a gain in seeing, connecting and communicating. The book calls these chains of consequences cascades. (The Kinedu data show the order in which skills tend to appear; that one causes the next rests on the wider body of developmental research.)

What changes after the first year?

The areas separate, and you can see it: a toddler can speak in short sentences and still tumble when she runs. That isn’t imbalance; it’s differentiation. It is also why comparing children gets harder, as I cover in The range of normal is enormous.

What does this mean for parents?

In the first months, there is no “just” playing or “just” talking. A coo and a smile, a bath with you talking, a game of peek-a-boo: each does several jobs at once (see Bath time). As your child grows, watch for cascades: when something new appears, ask what it opens up next.

Being strong in one area and still working on another is usually a common pattern, not a problem. If an expected skill still hasn’t appeared after several months, or she stops doing something she could do, talk to your pediatrician.

The full “why,” including where this finding came from, is in Chapter 2 of Big Bang Baby. You can read the Introduction free.