One-third of all kids -- including 24 percent of 2- to 4-year-olds -- are now overweight or obese, according to the Robert Wood Johnson Foundation. In an age when the most common vegetable eaten by toddlers is a french fry, experts say that the way we are feeding our children is laying the groundwork for a lifetime of heart disease, diabetes, and other serious health problems. It's frustrating that many of the factors contributing to the obesity epidemic -- from huge restaurant portions to vanishing phys ed classes -- seem to be out of our control. Fortunately, research has revealed these simple ways to help prevent kids from putting on too many pounds.

Get Moving

Kids should be active for an hour a day, and it's best to spend at least some of that time outside. "They're more likely to run and jump outdoors than in the living room, and one high-energy activity leads to another," says Sandra Hassink, MD, chair of the American Academy of Pediatrics' (AAP) obesity task force. Start with just 15 minutes a day. Store jump ropes and tennis rackets in plain sight, and keep rain gear handy, so kids can go out on rainy days, too. Try to inject more physical activity into all aspects of daily life: Get your toddler out of his stroller more, have a limbo contest after dinner, play hopscotch while waiting for the school bus.

Adopt an All-for-One Strategy

The most effective way to improve children's habits is to make lifestyle changes as a family -- and emphasize wellness rather than weight. If your kids question new menu items, just say, "We're trying to be a healthier family now, so we can all have more energy." That way, a heavier child won't feel singled out, and normal-weight kids will get the important message that they need to pay attention to their nutrition and fitness too. "Research has shown that if parents don't change their habits, kids won't change," says Dr. Jacobson.

Stock Up on Fruits and Vegetables

The more you serve them (and eat them yourself), the more likely your kids will be to grow to love them. Keep plastic containers of cut-up fruit and veggies on a low shelf in the fridge where your kids can see them when they're hungry. Be patient, since a child may need to try a new food up to 10 times before accepting it. Research has also shown that gardening makes kids more interested in eating the fruits (and vegetables) of their labor -- so follow Michelle Obama's lead and get sowing.