I would advise you to not show him the agitation or act as if stuttering is a bad thing at all. Show him theres nothing wrong with him, thats important especially coming from his mom, more important than the therapies and everything. If it does not go away in childhood like most people then i hate to announce to you thats another life destroyed by stuttering. The experience (frustration and everything) will only get worse the older he gets, theres nothing good about stuttering.