Honestly, the only age limit there should be is for hunting alone. If the adult is right there by the kid, I see no problem.
I remember going hunting with my dad when I was under 12 (the huting age here), the two of us only carrying one gun, and me shooting when we seen somethign. Nothing bad is going to come of it, the kid is under the adult's control.
Now, if you let 8 year olds hunt on their own, there is more of an issue.