London ? Doctors may soon have a prescription for health that even kids will like: more playtime.

European and international health experts say a new study makes the most convincing case yet for the benefits of children being active. They say the research may lead to new guidelines saying youngsters between ages 5 and 16 need to be active up to 1 1/2 hours a day.

For some parents, that might be accomplished simply by showing their children the door.

“Just making sure children play outside will double the amount of physical activity they get,” said Dr. Lars Bo Andersen, lead author of the research published today in the medical journal Lancet.

Experts said the study doesn’t mean children need to be on treadmills or in soccer leagues – they just need to be able to run around and play physically, even for short bursts of time.

The study looked at 1,732 9-year-olds and 15-year-olds from Denmark, Estonia and Portugal. Physical activity was monitored for four consecutive days. The more active children had healthier numbers for blood pressure, cholesterol and insulin.