A bout 21 percent of children ages 6 to 17 are obese, according to National Health and Nutrition Surveys III. Studies show that overweight kids are more likely to become hefty adults. And obesity in adulthood increases the risk of diabetes, heart disease, stroke, certain types of cancer and other chronic disorders.

The National Association for Sport & Physical Education (NASPE) in Reston, Va., recently issued guidelines recommending that children ages 6 to 11 exercise a minimum of 30 to 60 minutes per day. Ideally, the association encourages more than 60 minutes and up to several hours of exercise. This includes periods of moderate to vigorous activity lasting 10 to 15 minutes or more.

Others prefer a less rigid approach. Steven Anderson, M.D., of Seattle, cautions that the old rule of thumb - 20 to 30 minutes of continuous aerobic activity, 3 to 5 times per week - was designed for adults and may not be appropriate for kids of all ages. "We're not recommending that you get out a stopwatch or put a chart on the refrigerator," says Dr. Anderson, chair of the American Academy of Pediatrics' committee on sports medicine and fitness. "Our goal is simply to promote physical activity in as many ways as possible."

According to Judy Young, executive director of NASPE, "Physical education is only part of the solution." Just as parents reinforce good reading habits, they also should encourage their children to incorporate physical activity into their daily lives.

Here are seven ways you can motivate your kids to exercise.

1. Make exercise fun.
Find activities your child enjoys. Jodie Lefferts of Glenside, Pa., says her 12-year-old daughter, Cindy, wanted to be a runner like Mom and Dad. There was just one problem: She doesn't like to run. Lefferts told her daughter, "You don't need to run. Just find something you enjoy to stay active." Cindy soon discovered that tennis was her sport.

2. Set a good example.
Parents who are 20 to 30 pounds overweight send mixed messages to their kids about the importance of fitness. Tony McShane of Evanston, Ill., believes in motivating kids by being a good role model. An avid tennis player and triathlete, McShane is careful not to push his interests onto his children. Although he "would love it" if his 9-year-old son played tennis, McShane is happy Collin is enjoying other sports, such as soccer, football and basketball.

3. Exercise with your kids.
While McShane enjoys team sports, he also delights in unstructured activities with his three children. Typical family events include bike riding, tossing a football and playing basketball.

Says Dr. Anu Sheth, a pediatrician in Atlanta, "The whole family has to be involved." Parents shouldn't sit on the couch and tell their children to go out and play. "To motivate kids to exercise, you need to do it with them," she says.

4. Turn off the television.
"Clearly, TV is one of the major culprits," says Anderson. "The number of hours kids spend watching TV is mind boggling."

For many working families, it's difficult to find that balance. Young cites the lack of affordable daycare as a major obstacle. "Kids are being left unsupervised at earlier ages," she says. Because of safety concerns, many kids are left to watch TV and do their homework until their parents come home. Ideally, kids should be active after school and study later.

5. Look beyond organized sports.
Anderson says he's not convinced organized sports are the answer for all children. "Many team sports don't fulfill the requirements for aerobic activity," he says. Sure it's OK to play baseball. But except for a few short bursts, your child may spend most of the time standing around.

Lefferts has cut back on organized sports. For a while, her kids were so busy that they didn't have time to just play. Now on beautiful spring days, her girls will go in-line skating, play badminton in the back yard or jump rope.

6. Talk to your child's P.E. teacher.
Ask about your child's P.E. program and how you can provide support. If your child does not have P.E. or the current program is not enough, encourage your school board to make it a priority. Currently, Illinois is the only state to require a daily P.E. program for children in kindergarten through 12th grade.

Most important, P.E. should be fun. "You do a real disservice when you use physical fitness as punishment," says Dean Welsh, an elementary P.E. teacher in Junciton City, Kan. It's a bad sign if a teacher orders a student to run 10 laps for getting into trouble.

7. Remember that physical activity and proper nutrition go hand in hand.
Welsh sees more overweight students in what he calls "the Nintendo and fast-food generation."

thousands of junk-food commercials each year.