Many of us have fond memories of playing outdoors as kids, of running around, creating worlds, and tearing them back down again.

Experts say many kids today don't have the same play opportunities — and it's hurting their development and health.

A Philadelphia conference this weekend is trying to bring back play. The group organizing the conference is called "Philadelphia Declaration of Play" and its message seems almost too simple: kids need to play.  But organizers don't mean clicking away on a computer or structured, carefully supervised playgroups. And they certainly don't favor play that tries to sneak in learning how to spell or singing along to Beethoven. 

"Play that is freely chosen, and personally directed," explained Bryn Mawr child psychologist Marjarie Bosk. "The child knows what they want to do and is allowed to explore and play, and not directed and taught and pressured."

Bosk is one of the founders of "Philadelphia Declaration of Play" and helped organize the conference. She says research shows that free play allows kids to learn. "Children who have a lot of child-initiated free play do better academically throughout their academic lives, they do better socially and emotionally."

Naomi Roberson is programs director at Smith Memorial Playground and Playhouse in Philadelphia's Fairmount Park. She says when kids are playing, they learn important skills. "Little children like to pinch things, or play with tape, or with rice, so that's their fine motor skills," she explained. "They learn social norms, when playing with each other, learn how to problem solve, and how to communicate with each other."

Bosk and Roberson say their group is talking with parents, educators and city planners to emphasize the importance of play, and figure out how to create the space and time for it.