I mentioned this yesterday, but I really have no understanding of how social norms of parenting have changed so much. "Stranger danger" is hardly real. Car accidents and abuse by family members are real. Most 9-year-olds are perfectly capable of being on their own for some length of time without lighting themselves on fire. A playground filled with children and adults is not actually a dangerous place.
When I go back to the neighborhood where I spent some time growing up, I'm always struck by the fact that I never see any children outside, ever. Maybe that's just changing demographics and there aren't any children. But when I was a kid we'd wander around, ride our bikes, go into the "woods," go down to the creek, play street hockey in the middle of the road, etc. This was all normal. I didn't usually walk to school - there was a bus - but I would have been allowed to. It was about a mile.
