I believe they went swimming at Miller's Pond. There were several vacation spots mentioned, including Friends Lake, Shadow Lake, Crescent Lake, and Crystal Falls. I don't know the name of the park where they played sports. Could it be simply City Park?
In my previous question, I asked for Beaver's elementary school. It was Grant Avenue Grammar School.
Friends Lake was the one usually mentioned. The athletic field was Metzger's Field. Your turn.