PHILADELPHIA (AP) — In a darkened room at CHOP Primary Care, Cobbs Creek, physician Chris Renjilian set up a projector and debriefed doctors, nurses, and other staff on a new intervention that the office will begin offering to patients in its care.

The medical breakthrough in question? Prescription-strength outdoor play.

"As primary-care pediatricians, one of our goals is to help children get more active. The American Academy of Pediatrics recommends 60 minutes a day of outside play," he said. "This is something we already spend a lot of time screening for and talking to families about."

Now,...