A place for kids to play and hang out which isn't bubble-wrapped.
It's not really the nanny state, it's tort lawyers driving the nonsense. We did wild and crazy things when I was a kid, including BB gun battles and stone-throwing battles. We made bonfires in the woods, and swam in the reservoir in our underwear. We stole our parents' cigarettes and smoked them in the woods. Of course, that was not on school property. I was a tomboy.
We broke our arms and our legs, got banged up, and got lost. Good adventures, good training for life. I got to the point where getting lost was a fun challenge.