I was at the range the other day and saw a couple who had their son there, who was barely able to walk (I don't remember how many months he was). they let him fire a muzzle loading pistol that they had (Caps only of course) and that kid absolutely loved the sound those caps made (didn't mind the other rifles going off either). He also had a death grip on that thing, woulden't put it down for a second.
I love seeing kids at the range, their just so lucky to get to shoot guns at that age.