Hickock45 on Child Gun Safety:
I was given a BB gun and instructed not to point it towards people or birds. My family never really discouraged shooting at squirrel, but I shot at cans a lot. Eventually I would start shooting a Ruger 10/22 and then got a Henry.
They need to understand that guns can be incredibly destructive and easily end something's life, person or animal. Never point a gun at anyone or anything they do not intend to shoot. Guns can be dangerous in dangerous hands.
Take him to the range with you after explaining good safety practice and demonstrate good safety practice. Give him a bb gun. if he will do as he is told in treating it as he should a real gun in a safe manner, he gets to shoot a .22 at the range under close supervision.
This is how I learned firearm safety, and none of the guns in our house ever had locks on them, and I did not get into them because I knew that they were not toys. Taking the mystery out of firearms will do so much in keeping them out of them when they are not being supervised.