By Stephanie Stahl

PHILADELPHIA (CBS) — Time to get moving kids! New research says senior citizens are often more active than many teenagers and smart phones get much of the blame.

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Experts say technology is a big reason why kids are so inactive, which is linked to the obesity epidemic.

According to the CDC, more than 12 million American children and teenagers are overweight.

“Try to encourage them in any way you can to get outside and do more activity,” Dr. Jennifer Brubaker of Cleveland Clinic Children’s said.

A new study found that on average, 19-year-olds are about as active as sedentary 60-year-olds.

The study looked at data from more than twelve-thousand participants in a National Health and Nutrition survey.

“We want them to be active, you know, getting sweaty, getting short of breath; really pushing it and trying to do the most that they can,” Brubaker said.

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Brubaker said 60 minutes of activities is ideal for teens.

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In addition to being overweight, sedentary teens have an increased risk for a variety of health problems, including heart disease, diabetes and cancer.

Doctors say to encourage more activity, parents should have some rules about technology.

“Setting limits, healthy limits for screen time; making sure your kids aren’t sitting around all day long on their screens,” Brubaker said.

Doctors say one of the best ways to combat the obesity trend is to get the whole family involved in physical activity — whether it’s with a regular exercise routine or participating in sports.

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Or maybe teenagers need to hang out more with their active grandparents.

Stephanie Stahl