WASHINGTON — Grilled chicken replaced the hot dogs. Strawberries instead of cookies at snack time. No more fruit juice — water or low-fat milk only. This is the new menu at a Delaware day care center, part of a fledgling movement to take the fight against obesity to pudgy preschoolers.

Day care is the next frontier: New Harvard research shows few states require that child-care providers take specific nutrition and physical activity steps considered key to keeping the under-5 crowd fit.

And while years of work now have older kids starting to get healthier food in schools, more and more kindergarteners show up their first day already overweight or obese.

"We’ve got to start really early. Elementary school is too late," Dr. Lynn Silver of the New York City Health Department — a leader in anti-obesity standards for day care — told a recent meeting that brought child-care specialists together with federal and state health authorities to start learning how.

This isn’t about putting youngsters on a diet. It’s about teaching them early, before bad habits form, how being active and eating healthy can be the norm — and that junk food, including the chicken nuggets-type fare that we call "kid food" — should be a rare treat.

"This is a whole new way of eating for our kids," says Maria Matos, who heads the Latin American Community Center in Wilmington, Del., and has overhauled what she now knows wasn’t an ideal preschool menu even though it fully complied with day care regulations.

It took some adjustment. Matos started serving Latino dishes with brown rice instead of white. The mac-and-cheese got a wheat makeover, too. Many of her youngsters had never even seen honeydew and kiwi, and had to be coaxed to try it.

"You have to get people used to this different type of eating," she says. "Some are there, and some are still getting there."

Two-thirds of Americans are either overweight or obese, and it starts shockingly early. Research last April found almost one in five 4-year-olds already was obese. Rates are highest among American Indian, Hispanic and black children, but the problem affects every demographic.

Nearly three-fourths of children ages 2 to 5 spend at least part of their day in child care, about half in formal day-care centers.

That makes day care a vital next front, says Debbie Chang of the Delaware nonprofit Nemours Health & Prevention, which helped push that state to adopt a list of new child-care licensing requirements to do just that.

"Everybody is always pointing fingers at us parents saying, ’You should do better.’ A lot of other people are feeding our kids," agrees nutrition specialist Margo Wootan at the Center for Science in the Public Interest.

Such mandates aren’t common. Harvard researcher Sara Benjamin compiled a top-20 list of nutrition and physical activity regulations that health specialists call key. They include:

—At least 60 minutes of structured physical activity and 60 more minutes of active free play.

—Not letting children sit for more than 30 minutes at a stretch.

—Only 1 percent or fat-free milk for kids 2 and older.