When I was a kid we used to swim at the local MDC pools in Boston. It was $.25 for kids and I think $.50 for adults. Anyways, my mom would drop my brother and I off sometimes and go to work across the street. So we'd be there from like 1pm - 2:30pm by ourselves, just swimming. It wasnt a big deal then. They had lifeguards.
I guess nowadays, as a parent, I would be worried about drowning. We have a community/neighborhood pool that we share with about 40 households and the pool lot is adjacent to our lot. I worry about the kids swimming there as they get older (teenagers) and we arent home. But I guess there has to be an age when you dont escort your kids to the pool, right? When I was a kid I guess it was 11 or so....