Philadelphia is absolutely an option, but it depends on the neighborhood. Eg if you live in the penn alexander, greenfield, or meredith catchments you have a great elementary/middle school and there are lot of kids of late elementary/early middle school age moving around the city independently.
I live in west philly and it is great: the park is excellent and lots of kids safely go there by themselves, the local school is very good. Transit (specifically the trolley) is good and safe.
I live in west philly and it is great: the park is excellent and lots of kids safely go there by themselves, the local school is very good. Transit (specifically the trolley) is good and safe.