Mt. Lebanon! Park at the library. You can go up hazel and around the neighborhood back there. Not flat, but a good place to park and go out, tons of kids, sidewalks, super safe, and almost every house hands out candy (I live there).

Screw everyone who's commenting that you can't come into other communities. Despite Lebo's reputation as a bubble, there is not a single person I know who would bat an eye at someone bringing a kiddo from another neighborhood to trick or treat.