It might not be the parents themselves who are reluctant to have their kids meet with you. The parents of kids I used to play with in grade school have often tried to invite me over through my mom. She always refuses on my behalf because she knows I can't handle social interaction except under specific circumstances and would refuse the invitation if given the choice. And since these kids are older, many of them might not like the idea of having such things set up for them anyway. If you're set on helping autistic kids, there are programs set up for that, like those "big brother" organizations. No need to gripe about the parents - sorry if I sound rude, but my mom's parenting has been very badly and unjustly criticized by people who don't understand my needs. I prefer that parents of autistic kids be given the benefit of the doubt, NT or not.
_________________
I have not the kind affections of a pigeon. - Ralph Waldo Emerson