But "on their own" doesn't mean all alone. "The babies who did best had parents who were present during play but who didn't run the show," says P. Nina Banerjee, Ph.D., study author and a researcher at Columbia University in New York City. When you can, step back and watch how your baby is playing with a toy before jumping in. More explorer tips:

Let him chew. "Mouthing a toy is the first way babies learn," says Banerjee. If your baby is munching on Good Dog, Carl, say, "That book feels good on your gums."

Describe the toy. "Looking is the next step," she says. Imagine encountering an alien spaceship. That's how your baby approaches the world, so have fun pointing out a toy's details to get him to take a closer look.

Quiz him. Your 6-month-old isn't going to fit a square into a square hole. Instead, ask, "What else can you do with it? Bang it?" This way, rather than taking over, you plant the idea that there's more he can do with it.

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