That's a sad event, and there weren't many details, due to the investigation. I'm guessing there wasn't enough experience with firearms involving the boy. I grew up around guns, and my dad wasn't afraid to show me the guns, take me to shoot them, and tell me where they were, where the ammo was, ect. Growing up, it was just a common thing, and I wasn't "curious" enough to go digging because he would take me to shoot whenever I wanted. Because we were around firearms and had access to them, even when we got in fights (me and my brother, or with friends) we didn't run up to find a gun. We knew them, learned how to use them, and knew what they would do and the consequences.
Education and experience is the key to safety. Avoiding teaching children about them gives way to curiosity caused by TV and movies and games. Guns seem fun because you can shoot people in a game, and just restart.