What struck me is that they only see him at the park. That the kid plays with the 8 year old at the park. I don't see where he's hanging around anywhere other than the park.
A kid in your neighborhood you can't necessarily escape, but the parents should be able to solve that.
This is happening at a park. So, stop going to the park.
Homegirl, what you're describing, that's my son. He plays with all the kids in the neighborhood, when he has nothing better to do. He doesn't seek them out. He'll go outside to ride his skateboard, or his bike. We live in a culdesac with a lot of kids. As soon as the little ones see Jared, they come running. If he feels like it, he'll play with them, but most times he ends up coming inside because he's got 10 little kids screaming around him, asking him to pay attention to him. Overwhelming.