Because babies are now spending so much time on their backs, many are experiencing "flat head syndrome"; weak arm, neck, shoulder and trunk muscles; and delays in developmental milestones such as rolling over, crawling, pulling up to stand and walking. The estimated 60 waking hours a week babies are spending in things (what a colleague calls "containerized") further exacerbates some of these problems.

Of course, nobody wants their child to go through life with a flat head. And lack of upper torso strength could result in difficulties with gross (large muscle) and fine (small muscle) control. The former is needed for physical activity and athletics and the latter for such tasks as writing and keyboarding.

Also, although babies do eventually master most or all developmental milestones, babies who don't spend time on their tummies may spend less time crawling. This could mean eventual difficulty crossing the midline of the body – the invisible, vertical line that runs from the head to the toes and divides the body into left and right sides. In some cases, children unable to cross the midline – and there seem to be more of them in schools every year – have problems with reading and writing.

The good news is that something as simple as tummy time can lessen or eliminate all of these potential problems. Pediatricians advise that even five minutes of tummy time a day have a positive effect on head shape. When you place your baby facedown, curiosity induces her to attempt lifting her head and pushing up on her arms, strengthening the upper torso. (When she's on her back, she has no compelling reason to make the effort!) And crawling is a cross-lateral experience (the left arm and right leg move simultaneously and vice versa), so children who spend time practicing this motor skill generally have no problem crossing the body's midline. Also, babies who spend time facedown tend to reach their motor milestones earlier than babies who don't.

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