As a parent, I am ultimately responsible for the safety and well being of my children. An 8 year armed with a fully automatic weapon is a recipe for disaster. Even if the 8 year old has the proper safety training, a weapon that fires continuously with the pull of a trigger is too much to handle without an adult to be hands on with the juvenile.
Dad is ultimately responsible for choosing a weapon that was beyond an 8 year old's control. Its a tragedy, and the dad will will have to bear that grief on several different levels.
This is just sad. A child in the grave because his parent failed him.