Preschool teacher Jennifer Rosario serves celery to 2-year-olds at the Latin American Community Center in Wilmington, Del. New research from Harvard University shows few states require that child care providers take specific nutrition and physical activity steps to keep the under-5 crowd healthy.

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.

Although years of work now have older kids starting to get healthier food in schools, more and more kindergartners 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.

Starting early

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.

Healthy habits

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.

• No more than 6 ounces of 100 percent juice a day.

• No sugar-sweetened beverages.

As of last January, Benjamin found Idaho and Louisiana with the fewest such requirements and Delaware, Georgia, Alaska and Nevada with the most.

Among Benjamin’s most disappointing findings: Parents might describe this as the age of ants-in-the-pants, yet an average day included less than an hour of moderate-to-vigorous physical activity. Her team visited one Rhode Island day care last fall where the kids didn’t get to run around at all when it rained.

Most states merely require that children “be active throughout the day. What does that mean?” she asked the recent Nemours meeting.

Massachusetts last summer imposed a 60-minute activity rule. Now Benjamin’s team is testing how day cares implement that change.

Training providers is key, says Nemours’ Chang. Many simply don’t know, for instance, that whole milk is unnecessary extra fat for preschoolers while low-fat costs the same.

How much should a preschooler eat? An easy-to-use Web site gives specifics: mypyramid.gov/preschoolers. Generally, a preschool serving size is about 1 tablespoon of each food type for every year of age. Proper portion sizes were a surprise to Maria Matos, who bought serving spoons pre-measured for preschoolers so they can dip while teachers tell how a colorful plate is a healthy plate.

Matos says the changes cost a bit more; she hired an extra part-time cook to make more from scratch, and fresh foods can cost more than processed. Chang and Wootan say day cares can make many cheap changes — swapping water for juice, for instance. But it’s an issue that Nemours is pushing Congress to tackle as it reauthorizes the Child Nutrition Act later this year, which helps fund food at low-income day cares.