How do you, kindly, deal with an annoying child that won't leave you alone?

Move to the next state over

Lock your door next time you’re jerking it to trap hentai

Yes. It is a child, of course, age 5, and they don't have a concept of boundaries yet.

The child is legally and ethically not my responsibility, numbnuts.

So, you're in a situation where you are unable to avoid this kid whatsoever? I would say go to the parents again, because violence wont solve anything in this case. Explain that the kid wont leave you alone. This is pretty ignorant on the parents end if you ask me.

Bring your toys and have a playdate

I would love to do that, but I don't want the emotional ramifications of guilt after doing so and my biggest fear; having the police involved.

Obviously I wouldn't resort to violence, but I guess I could try again with the parents, for the 3rd time.

Have you tried to ignore the cild for a couple of days? He will be bored eventually and will leave you alone in the future "because you're no fun"

here's a tip : BE BORING! kids dont want boring in their lifes
the same aplies for crazy people