Don’t know why the fact that the gun jammed twice before firing is of any impact to the story. Obviously the 15 year old was successful in clearing the jam. Unfortunately for the little one the weapon functioned properly. An eight year old should be introduce to a .22 long rifle first. I can’t see introducing a kid to a pistol or submachinegun at all. Seriously, “you’ll shoot your eye out kid”.
It is ALSO a good idea, when shooting full autos, to start with just 2 cartridges in the magazine, at first, to get a “feel” for the recoil, and rate of fire. Then go to three, then 4 or 5, and 8 or 10, etc. Had they done THAT, the boy would now PROBABLY be alive, because it would have been apparent after the 2 shots fired, that is was too much gun for him, at that age.