Here's a picture of my son with the products of his first big date with a plasma arc welder. He's older than nine, of course, but he started using air hammers, drill presses, and hammer drills when he was around eight. He started using a die grinder when he was ten. These tools are useful, but can maim or even kill if handled poorly.
So why does this not feel the same as putting a automatic weapon in a little girl's hands? Yes, an Uzi is a dangerous object with notorious muzzle climb that a small child is inherently going to have trouble controlling. By comparison, a hammer drill has a much more limited potential to get out of hand.
But that's not the salient point. A hammer drill is a tool for making holes in concrete and such. That's what we use it for. I taught my boy to use it so he could do real work with it around the place. An Uzi, in contrast, is a weapon of war. There is no target shooting class you can use an Uzi in, certainly not in full-auto. Blowing through a clip on an Uzi is not a sport. A civilian shooting an Uzi is taking a soldier's tool and treating it like a toy. Part of what seems so wrong about the Nevada shooting is that the little girl wasn't learning the sport of shooting: she was playing the game of war with a real weapon, and the weapon worked as designed.
I'm guessing my mom learned to shoot when she was around nine. I learned when I was a little older than that. I like going to gun ranges and shooting guns. If I didn't have a bad feeling about killing things, I'd probably hunt. So I actually kind of understand why parents would take their nine year old girl to a gun range. Kind of. Maybe twelve would have been better. And I understand that guns are pretty important to them, so in the same way I want my son to know the tools so he can be a maker and make things, they want their girl to be a shooter. I cringe at the idea of putting firearms at the center of your identity, but I can't pick for somebody else.
But treating weapons as toys is a problem, and this incident shows one reason why. There is a little thrill of focussed attention that never goes away when you are handling a dangerous object, but if that thrill becomes the point, and you start needing bigger and bigger hits of it, then your hobby is more than just a hobby. This is so far away from target shooting as a sport. There is no sport here, only playing dangerous games.
Condolences to the survivors of the incident in Nevada.