I've been playing with You Tube videos and I've uploaded this clip of grandson Quinton firing the AR-15. He was six years old at the time and, of course, under proper adult supervision. The little clip is 22 seconds. Notice at about 19 seconds where he turns his head to make sure his uncle is wearing hearing protection.
Quin mentioned this video at school and won serious "cool points".
It's one of my favorite grandkid videos.