To be honest there’s not much you can do, speech pathology might help his confidence a little bit, medication definitely won’t do anything. The best thing you can do for him is make him feel loved and accepted for who he is. There is a good chance he’ll stutter for the rest of his life so if you start now and make sure he’s confident in himself, he won’t struggle as much as an adult. When you have a stutter loving yourself is half the battle