"Down, Mommy. Down!" Julie strained to be put down so she could scoot along the floor and undoubtedly discover something new to put into her mouth. At ten months old she had grown adept at getting around by scooting along on her butt, and in that way she seemed to be able to move a mile a minute. Why crawl when you can get around hands free?

"Hold on, baby." I carried her into the family room, which we had cordoned off with baby gates. She kicked her chubby legs clad in tiny ...