I don't know this friend or his parents at all.
DS is inviting him to his birthday party so hopefully I'll meet them then.
I will echo DeeDee in saying that just the fact that you are inviting him to the party is already a step forward. It also gives you a natural way to contact his mother to start a dialog like the one that Portia suggests. You could email her and tell her that your DS has told you that her son has autism, and you just want to know if there is anything you can do to help him have a good time at the party. Is he on a special diet? Might he need a space to retreat into? Would it help to tell him what the schedule of events at the party is going to be so he knows what to expect? You want him to have a good time and you recognize that you might need to provide something different from what you normally would to make that happen.
There are a lot of books out there with autistic protagonists that it might be good for your son to read, but be sure to caution him that just because the kid in the book has a particular trait, that doesn't mean that his friend will have the same one. Autism is something that manifests very differently in different people.
