When I was around that age I had a step sister who had a similar issue, including lots of aiming the gun at my father and I. I think part of the issue can be that they are forgetting the steps, or the rules, because of anticipation of shooting.
I haven't taught much shooting to younger kids, but I have done it a bit. The way that has worked for me is taking the steps and ritualizing them. Having a safe place to set the pellet gun, a steady and easy to grab supply of pellets, and making them verbally repeat the steps after I say them, as they are performing them. We do a lot of the same thing in Martial arts, even while teaching them archery. Maybe that helped, I'm no pro.
