Cities began building playgrounds in the late 1800s and early 1900s as a way of getting young children out of traffic and older ones away from delinquency. In time, the physical spaces were joined by recreation programs organized by nonprofit organizations. Today, it’s not only children who use America’s publicly owned playgrounds, athletic fields, parks, and streams. Tens of millions of adults do, too. And for our access to inexpensive recreation, we can thank government.