How Babies Work

The One Thing Standing in the Way of Your Baby Walking

Little baby stands up on her feet

You’d have trouble walking in one of those, too.

Photo by iStockphoto/Thinkstock

So let’s say you’re a baby. You really want to walk, but walking turns out to be hard—stunningly hard. And then it hits you: This would be a lot easier if your parents hadn’t stuffed this big heavy bag of warm pee between your legs. Is this some sort of practical joke?

Most of development is invisible: You can’t see a theory of mind take shape. But when a child moves, the magic is all on display. And if you watch closely enough, you can see how the rabbit gets pulled from the hat—how an infant learns to walk even while carrying his waste around with him.

For a long time, no one would have described motor development as magical. It’s a subject that was once thought to be dull and obvious. The psychologist Arnold Gesell proposed that motor development happens in lock step with neural development, and that theory held sway for decades.

But motor development turns out to be a highly variable and creative process. Dull and obvious are exactly the wrong words for it. Instead, babies learn to move in a wondrous array of ways. In Baby Meets World, I discuss the wonderful work of Karen Adolph, a psychologist at New York University who studies motor development. Adolph’s laboratory offers an extraordinary vantage point for seeing just how infants move. To see how they adapt to new obstacles, she’s devised highly colorful experiments—lead-weighted shoulder packs, walkways that turn into foam pits, Teflon-soled shoes. Reading her work, as I write in the book, you imagine her laboratory looking like the set of a Nickelodeon after-school special.

Adolph’s studies shed light on what new parents see everyday—the nearly Sisyphean task of learning to walk. (Stand up, stumble, stand up again, stumble again.) And Sisyphus had it easy: He never had to wear a diaper.

A just-out experiment from Adolph’s lab tracked how babies walked while wearing cloth or disposable diapers and while naked. Carrying your pee around is not a good strategy. While in diapers, babies take shorter, wider steps. They are three times more likely to stumble or fall. Their gait is far clumsier. (This is true for both kinds of diapers, but especially true for the “old-fashioned, thick” cloth diaper.) But once they took off their diapers, their walking was immediately more skillful. Without a diaper, their stride was, almost instantly, much more mature—sometimes years more mature.

In other words, once freed from the albatross of that bag of pee, babies walk less like babies. This is interesting on a couple of levels: First, babies learn with astonishing speed—without a diaper, they immediately recognized that they could walk more efficiently, even though many of them had never done it before. Second, what we think is cute about babies walking—and babies walking is pretty much the pinnacle of cuteness—may not have that much to do with the baby. You’d walk funny in diapers too.


Nicholas Day’s book on the science and history of infancy, Baby Meets World, was just published. His website is He is @nicksday on Twitter.