Experts in childhood nutrition aren't surprised by a poll this summer that shows 50 percent of parents who have overweight or obese children don't realize their children weigh too much.

Many parents are in denial about their children's weight because they don't want to have to change their own eating and exercise habits, says Keith Ayoob, a registered dietitian who works with overweight children and their families in New York City.

Parents frequently ask him whether their children have a thyroid problem, but that's rarely the case. "It's usually a dietary and lifestyle issue. It's very difficult for parents to confront their own food issues," Ayoob says.

An estimated 25 million children in the USA are overweight or obese, which puts them at risk of developing type 2 diabetes, high blood pressure and other health problems.

A "Consumer Reports" magazine poll released July 25 of 3,048 parents who have children ages 5 to 17 found that 91 percent say childhoor didn't mention it.

Many parents simply don't realize their children are overweight, says Dawn Jackson Blatner, a registered dietitian in private practice in Chicago and spokeswoman for the American Dietetic Association. "The doctor never told them. Other kids in the class look like their child, and their kid seems pretty healthy," she says.

She has parents go to the calculator on the Centers for Disease Control and Prevention website (www.cdc.gov/nccdphp/dnpa/bmi) to figure out whether their children are too heavy.

Ayoob suggests families do at least three things immediately:

Practice the "Rule of One."" Limit children to one of each item served at dinner, such as one scoop of rice and one piece of chicken. But they can have unlimited amounts of vegetables.

Get moving." Make sure children do some kind of physical activity every day. They can start with 20 to 30 minutes, increasing gradually until they are doing at least an hour a day. They can walk the dogs, do errands on foot or ride their bikes.

Limit screen time (TV and computer) to two hours or less a day." "This is a must. The less screen time kids have, the more active they'll be."

Ayoob encourages parents to build on healthful foods their children already love. If they like snap peas, baby carrots or apples, offer them every day. Blatner tells parents to limit kids to 150 calories of junk food a day, such as an ice cream sandwich or a 100-calorie-pack snack.

"Kids shouldn't be solely responsible for making sure they get exercise and eat a salad every day," she says. "It's the whole family's duty to do it together."

For more on the "Consumer Reports" poll, visit www.consumer-reports.org/obesitysurvey.