I can relate, I'm really close w/ all of my neighbors. tho I dont have any kids, I've had to get out of some sit. where they were getting a little too close for confort but I like them and want to keep their friendship ; but something was making me uncomfortable.
when I get into situations where I feel uncomfortable with something, I just lie. I know it sounds bad, but a little white lie and some distance between you two for a month or so works. They get the hint, but its not enough for them to feel justified on being ticked off at you.
Tell her that you nor the kids will be there, then every time she calls, dont answer. Just for a couple weeks. That way, you are still close enough to be neighbors, but not close enough for her son to be coming over when you are not there.
Maybe???