Is it normal for a 2yr old boy to put his hand in his diaper?

Yes: If you mean he puts his hand in his diaper to play with his penis, this is normal. I would not shame him but it is ok to give guidelines about when this behavior is ok (in private, in bedroom, in bath) versus not (in public, etc).

Happens All the Time: This is normal behavior. It should not be critized at all. Teaching safety and privacy is something to take advantage of at this time.