Speaking of guns and impressing upon kids the destructive nature of them, when I was young my dad did something that I've never forgot. He took a can of tomato sauce, put it downrange about thirty feet and shot it with a 12 gauge. He told me, 'that's the kind of mess that will happen if you shoot a person with a gun'.
As for revolver or semi-auto, I'd pick revolver for two reasons:
1. Always easier to tell if they are loaded. You can hold the weapon properly and see the shells in the gun. I know the 'it's always loaded rule'...but we're talking kids here. A kid picks up the gun, knowing enough info to be dangerous, wants to check and see if its' loaded----well, much easier to tell with a wheel gun.
2. Manual of arms is easier. There is no having to remember 'is it drop the slide and rack the mag? or rack the slide and drop the mag? and then decock the hammer?
Kids with some info (enough to think they can operate the gun) can get confused with the details needed to run a semi-auto and get themselves hurt. A wheel gun is simple because if its' loaded, all you have to do is pull the trigger. To safe the weapon, hit the cylinder release and drop the cylinder out. Simple, easy, can't get confused about things.
That being said, the best choice is to have the gun locked up or out of reach of little hands. And yes, satisfy their curiosity and you'll have fewer problems. I've so far raised two daughters to adulthood with no mishaps and I'm have a 12 y/old and so far/so good.