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At 7 months, Zachary Miller was a happy and healthy, but not especially active, baby. "The pediatrician told me, 'The big ones don't like to move,'" says Zach's mom, Ellie, of Somerset, New Jersey. "She told me to put him on the floor and on his tummy as often as possible. He hates that. But it does get him to push up on his arms and roll over."

At 20 pounds and 27 inches long, Zach was already overweight. His height was in the 50th percentile for boys his age, but his weight was in the 75th (pediatricians like both numbers to be close together). But does it really make sense to be so concerned about a baby this young?

Yes, say an increasing number of health experts. The more weight a baby gains before age 2, the heavier she's likely to be as an older child and adult, studies show. If one or both parents are overweight, the concern is even greater.

And the eating and activity patterns learned in childhood  -- for good or ill  -- tend to persist for a lifetime. Some overweight kids as young as 3 or 4 can already have elevated levels of cholesterol, insulin, or blood pressure.

But many people miss the signs that a child (especially a boy) is too chubby. In one study, only 21 percent of the moms of overweight preschoolers knew it. As more and more kids get heavier  -- the average child's waist has gone up two sizes in the past 20 years  -- kids who are overweight increasingly look "normal" to us.

Pediatricians can miss the signs, too, even though the American Academy of Pediatrics (AAP) recommends that they check a child's body mass index (BMI)  -- a measure of fatness  -- annually starting at age 2.

So it's up to you to be alert to the signs that your child's overweight or gaining too quickly. "Our current lifestyle is putting kids at risk for serious health problems," says pediatrician Sheila Gahagan, M.D., of the University of Michigan's Department of Pediatrics and Center for Human Growth and Development in Ann Arbor, "but we can turn it around." The hard part: Improving their lifestyle usually means changing yours, too.

That means neither obsessive eating nor quick weight-loss plans, which are especially dangerous for children, whose growing bodies require nutrients from a broad variety of foods, including healthful fats. Instead, what's needed is a return to good nutrition centered on family meals, says Naomi Neufeld, M.D., a pediatric endocrinologist and director of KidShape, a family-based pediatric weight-management program in four states.

Here, what you need to know to set your child  -- from birth through grade school  -- on a path toward maintaining a healthy weight:

Jessica Snyder Sachs is a contributing editor at Parenting.

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