Rochester, Minnesota - Poor sleep quality is a factor in the increasing rate of childhood obesity in the U.S.  That's according to a recent study presented at a special conference on obesity and cancer by the American Association for Cancer Research. So what is the correct sleep duration for kids and how do you help them get a better night's sleep?

The right amount of sleep for your kids is important. Dr. Suresh Kotagal, a Mayo Clinic pediatric neurologist and sleep specialist, says, on average, kids in their early school years need nine to 9½ hours of good sleep. By the time they're teenagers, they need just seven to eight. And if they don't get enough sleep?

"One of the things that happens is stress hormones/steroids go up in the body," says Dr. Kotagal. "What do they cause? Weight gain."

Dr. Kotagal has three easy tips for kids to get a good night's sleep.

"I think it's, first, important to have a relatively fixed morning wake-up time," he says.

If teens have to wake up by 6 or 6:30 in the morning on school days, don't let them sleep in until noon on weekends.

"No. 2: Children should avoid napping in the day," says Dr. Kotagal.

When kids, especially teens, nap during the day, they're borrowing from night sleep and may experience difficulty staying asleep at night.

"No. 3: Exercise," says Dr. Kotagal. "Exercise is an amazing tonic for sleep."

It improves daytime cardiovascular function, raises body temperature and improves the sense of well-being that children need. It also makes them more ready to fall asleep at night. However, exercise should be avoided in the two to three hours before bedtime.