When President George W. Bush declared last week that better health is an important goal for Americans, he made a point of targeting children and adolescents. But pediatricians say it's the diaper-clad set we really need to watch. There's no exact measure of how much bigger babies have gotten over time, but doctors nationwide say they're seeing more and more infants and toddlers who are off the charts. "It's a tidal wave," says Naomi Neufeld, a pediatric endocrinologist in Los Angeles. (Average birth weights, an indicator of infant size, jumped to 7 pounds 7 ounces in 1997, from 7 pounds 4 ounces in 1970.) This growth spurt is related in part to the rising obesity epidemic among adults and children, but doctors say even healthy babies are bigger than they used to be: Amber Valletta's son, Auden--pictured on the cover of July's Vogue--is 18 months old, but "my doctor says he's the size of an average 3-year-old," the supermodel said recently. Julie Bruno, a lawyer in New York City, has a 9-month-old named Alex who, at 30 inches and 26 pounds, is nearly half his mother's height and is wearing the clothes of a 2-year-old. Often, these children are the products of taller-than-average parents (Auden's father is 6 feet 4) and good infant health--today's babies don't have to use their fat stores to fight off disease the way they used to. But in other cases, too much weight can impair development and lead to childhood obesity or diabetes. In general, babies should double their body weight in four to five months, triple it in a year and quadruple it in two years, says Fima Lifshitz, a leading expert on infant nutrition. In his own practice Lifshitz has seen a worrying surge in babies who exceed these guidelines. But parents of kids like Alex Bruno shouldn't be concerned; Alex may be huge, but he's healthy, and his weight is in proportion to his height. "I think he's perfect," says his mom.