I agree with jones, and would like to add that some young kids will simply 'experiment', which turns into a learning experience. Maybe your son is confused about his sexuality right now (and that would be okay since some kids just aren't sure if they like boys or girls when they are young). Counseling is a very good idea. In the meantime, assure him that you love him no matter what he does or feels.
find out if he was pressured into to, contact the parents of the boy