A generation ago, play was something most parents thought nothing about. On a nice day, parents would send kids out into the neighborhood in the morning, telling them to be back for dinner.
That's rare these days.
Recently, social scientists have studied what happens when that mixed-age group of kids play together, like the neighborhood gang of yesteryear.
Think about the friends you grew up with. Chances are, geography played a big part. You hung with kids in your neighborhood, all ages together.
But playtime that once happened organically is now often planned, like playdates, and almost always supervised.
Dr. Peter Gray, a developmental evolutionary psychologist studying children and play, said that when kids of mixed ages play together, there are benefits for all.
"Young children are naturally drawn to older children. They want to be able to do what older children do," Gray said. "And interestingly, older children are drawn to younger ones."
Gray found younger children gained academic skills from playing with older kids. They were encouraged to read words they didn't know and learned math when older kids had them keep score.
Older kids were more nurturing when they played with younger kids and more likely to engage in high-energy creative games.
Gray said parents and educators should encourage kids of all ages to play together. Start with a parent's block meeting and get the adults on board.
"One of the parents or maybe there's a grandparent on the block who's home, can sit out there and make sure it's just safe enough," continued Gray.
But they should not intervene. Let the kids hash out their differences on their own.
Gray also said parents can look for so-called "adventure playgrounds" that are being erected in major cities in the U.S. Places where kids can build things and design their own activities without parents looking over their shoulders.
There are notable adventure playgrounds in Ithaca, New York, New York City, Denver, Colorado and Huntington Beach, California to name a few.