The percentage of children who are overweight has more than doubled over the past 30 years. Although many factors are contributing to this epidemic, kids are becoming more sedentary. In other words, they're sitting around a lot more than they used to.

According to the American Academy of Pediatrics (AAP), the average child is watching about 3 hours of television a day. And the average kid spends 5 1/2 hours on all media combined, according to the Kaiser Family Foundation.

Parents need to ensure that their children are getting enough exercise. According to the 2005 dietary guidelines from the U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (HHS), all children 2 years and older should get at least 60 minutes of moderate to vigorous exercise on most days of the week.

It's also important to remember that young children should not be inactive for prolonged periods of time - no more than 1 hour unless they're sleeping. And school-age children should not be inactive for periods longer than 2 hours.