Clinical fact that children do not have the maturity to responsibly handle guns until late teens. As "mature" as some may seem, their brains are still developing and "mature" they are not. By definition.
I knew a "very mature" 15 year old kid who, at a deer hunting camp, was cleaning his "cleared and unloaded" rifle at the end of the day. In a act of spontaneity that even he doesn't understand, he put the "cleared and unloaded" rifle to his heart and pulled the trigger. Just for "fun." The rifle had a round in the chamber. It was a miracle that he survived a point-blank 30-06 shot to the chest.
This is the problem with giving kids firearms. The act out spontaneously and without logic. It's what their developing brains do, and no amount of parenting can change that. Naturally, every parent will tell you otherwise. Denial is not just a river in Egypt.
That is a ridiculous story. If you put a framing nailer in an untrained kid's hands they will kill themselves with that too. That kid did NOT know gun safety at all, and was improperly trained, period. My kid, who also shoots his friends with air soft rifles regularly, knows gun safety because I drilled it into him, and one mistake (which will not lead to an ND if you follow proper gun safety), equals one strike you're out. One is a toy and the other is a FIREARM, and he knows the difference. The idea that kids can't be equipped by adults to handle firearms is insane. My kid is more careful and deliberate than 90% of the people I hunt with, who are generally veterans with poor muzzle awareness, and bad habits. In the military you get so used to firearms that you need constant reminders about the pointy end.
I started hunting at about 6, but did not carry a firearm till I was 12. I carried a broomstick with a cloths-pin and a rubber-band basically simulating a hair trigger with no safety. It went off once when I laid it against a fence we were about to cross, and I had to wait at the car from dawn to dusk. It sucked, but it never happened again.
Care and supervision must be taken when letting kids shoot and hunt. Do that properly and there's nothing wrong with it. I can assure you that my kid at 12 would have snatched that rifle away from that "very mature" peer, just like I would have. That comes from lots of lessons learned that I TAUGHT him. First and foremost that ALL GUNS ARE LOADED. So basically if you forget the very first and most important rule you have not been trained, and should not touch a firearm.
As a case study that is an incredibly poor one, and a failure of instruction plain and simple. Everything in my safe is unloaded, and as my kid pics firearms out of it he clears every single one at first touch. When after clearing it in front of me I re-clear it in front of him when he hands it to me. Thus are habits formed and ingrained. At my local gun store we clear and reclear when passing a gun back and forth between us. Even after clearing, re-clearing, and re-clearing again the gun is STILL loaded.
If this isn't how you are trained, and you don't know this, then yes, you shouldn't handle firearms, because without proper instruction and good habits they CAN be dangerous. You must train yourself and anyone UI to good habits, because that is what makes it safe.