J.L.
All kids have germs and I wonder if you are concerned about germ infestation why you are babysitting. Have you talked to his mother? It seems to be a family problem and not just a babysitter problem. I don't want to seem harsh but if he is having teething issues he can't help it, and discussing with the parent should be the right thing to do. Maybe they should talk to his Dr. There may be underlying issues for him.