He should have cleared it with you first - that's something that will need to be discussed with your hunting partner. That being said - us hunters need to stick together - if he's just getting into things I would be honest with the kid. Tell him that it's great he want's to get into hunting, but that for saftey reason's etc. you just don't take anyone and everyone hunting. I would encourage you to invite him along but as a hunting companion only (no gun right now). That way he can help setup decoys, learn how things are done safely, etc. Make sure to explain things to him, how to be safe etc. If it doesn't work out - just don't invite him back.

We all had to start somewhere and if no one teaches him the right way to do things - how is he going to learn?