First off, screw the anti's. They will never be happy with anything we do, no matter what. If that bothers you, join the NRA, they like compromise and I'm sure they can offer you some tips on how to do so with them.
Personally, I think you should start their training the day they are born, and continue constantly up until you think they are ready for live rounds. Kids are learning sponges and are a lot smarter than many seem to think. Teach them and give them responsibility as early as you can and you will be WAY ahead of the curve. Your the programmer, if your kid turns out screwed up, it aint their fault.
Our kids fired "thousands" of rounds out of their Chipmunks on the living room floor before they ever fired their first live round at 4. By then, they completely understood the safety rules, and had most field positions down. The first time they shot, they put every round on the paper and most in the bull of a 25 yard pistol target at ten yards, offhand, standing on a chair to clear the bench.
Their whole time growing up, we NEVER had any problems with firearms,( other than draconian, PC, school policies and freedom of speech) or firearm safety. I trusted my kids at 4 and 5 more than a lot of adults I know.