While we do not know how old your son is. It makes the call hard to say along with if he has ever shot the 20 ga. at all or not. You should stay with the 2 /34 " shells if he is young which I am guessing he is. I surely would recommend holding him back to the 25 yard range as well. You want him to do great if one shows up. Heavy shots for your son maybe a bit much and cause him to flinch when shooting.. You surely do not want that. That is my 2cents worth.. As well as good luck to your son..