Thanks guys. I've talked to him and i'm hoping that he understands what I am talking about. But I appreciate everyones advice!
Totally normal. He has discovered that it feels good-plain and simple. :) Thank God right.
Yep, perfectly normal. He's not being sexual, it simply feels good. Like a good old back rub... Kids this young touch and check things out down there. Talk to him about privately doing it, that no one else should touch him and likewise, and try not to make him feel bad. You don't want him thinking his feelings are sick and perverted.
Normal. Teach him about privacy and tell him how it makes you feel when he does it in front of you. See numerous previous postings on this topic.