Spook, maybe I can add a little landowner experience. I allow kids accompanied by adults to hunt gophers here on the ranch at any time. It is a place where parents can mentor. They may hunt any non-game to gain experience. They should be accompanying parents on hunts to learn ALL the ropes before a firearm is put in their hands. On the flip side, if I allow legal kids to hunt pheasants here with their parents, the parents will hunt in competition with their kids every single time....the result is the parents limit out and kids get 0. I have a real weakness for a guy who drives in my yard with 2 kids and a dog to go hunting. I allow the kids to hunt but not the adult....result; the adult actually mentors the kids with "at the moment advice".
My experience tells me that parents are not all that good at helping during the hunt. My better half is a middle school counselor and collaborates with the local hunter safety instructors and all concur that while not all kids fit the mold, if you have to choose an age, 12 is it. There is both physical and mental readiness to consider. Hope that helps.