Now the gun. Okay, a semiauto is going to be better than a revolver for the kids. Here is what you do: Keep it right next to your bed, but keep the magazine and the gun apart. Very few kids have the sheer upper body strength to pull back the slide far enough to chamber a round, even if they knew the mechanics of the act, and tv doesn't teach ALL of this. Having a gun with a magazine disconnect can be a plus (just an opinion freepers hold flames, please) as an extra layer. How old are your kids? I taught my daughter gun safety and nomenclature from the time she was six. Taught her how to shoot at age ten and now she has a Ruger SP101 .357magnum to call her own. I only have to train her fiance to be as good as she is, now. I'll give you a little "exercise" we used to run in the army for the kids sense of gun safety at the end of this post.
Choosing a gun, especially a "first" gun is as personal as choosing a mate. My wife can shoot, but she's not the first person who will save my life...I AM. You've got to fondle a lot of "candidates" at the gun show. Involve your wife in this so she won't get jealous. Maybe look for a gun for HER, too. NOT the same one as yours! TRUST ME ON THIS! When you find the "right one" you'll know it beyond all doubt. It'll just feel right, like "Excalibur" and King Arthur. Your instructor can then teach you to shoot that one well. Generally speaking, you should choose the largest caliber possible that you can consistently "hit" with, because nobody ever died from a loud noise. The smaller the caliber, the more important shot placement becomes. I would advise against anything smaller than a 9mm and have the 45 at the top of the list. My daughter can handle a .357 magnum, and my 45's so recoil really isn't a problem, given a chance to be properly trained. However, I start all of my trainees on a .22 and slowly work them up to whatever caliber they have chosen, using my guns to bring them forward to the proper point so that they can start using their own new gun.
Stopping power these days is more a result of proper ammo than caliber, although good ammo and a .45 is almost unbeatable. All the major manufacturers have good ammo. But I'd go with whatever feeds the best in your gun and whatever produces the best groups. So you may have to spend some $$ figuring that out by shooting. Also, I almost always carry a magazine full of pre-frangible ammo like MagSafe or Glaser when I'm out and about to prevent a TNT (Thru-N-Thru) gunshot wound that may hit an innocent bystander if I get into a conflict of the personal and hostile sort which might also bring a charge or lawsuit after I survive. As a plus, this stuff from MagSafe and Glaser (there are others, but I carry those I've mentioned) is usually low recoil and low flash. But, it ain't cheap! Run enough to know where each round will hit at any given range out to say twenty meters.
The kids: TEACH THEM GUN SAFETY. The first thing is to show them in a dynamic fashion (I'm a professional educator with 15 years experience as well as a certified firearms instructor) because most kids are visual learners. That's why I make kids copy notes instead of letting them study the text, because the act of writing ignites the learning process. They hate it though, lol.
You're in a rural setting, so this should be easy. Take the kids out someplace where it's safe to shoot, even the local police range, if they'll let you do this demonstration. Get a Honeydew melon (green on the inside, yellowish on the exterior and smooth) and have each kid take a "sharpie" permanent marker and draw a face (VERY DETAILED: hair, eyes, ears, etc) and then tell them to concentrate very closely that the face they have drawn is that of their best friend! Next, have them put on eye and ear protection (use the little foam rubber throwaway plugs--protection, yet let some of the sound thru--just enough) and carefully allow them to take hold of the shooter's arm (if you don't think you can pull off a first round hit, get somebody who can) lightly and then totally blow that sucker to teeeeeny tiny pieces with a heavy caliber pistol like a .45 with high velocity defense ammo. Clear the range as safe, go down range and show them the pieces. TELL THEM: "This is what happens when you touch a gun without daddy being present." Next tell them exactly where you keep it and tell them you're trusting them like an adult to keep their friends away from there. It's a family secret. MY daughter used to go postal on her friends if they even got near our room during play times. She never told them why, but she knew the family secret that was where the guns were. She felt like she was being treated as an adult (powerful stuff to a little kid) and she treasured that. NOW, I still kept everything unloaded and LOCKED up except for the gun I had on my person, until I went to bed. You can put key locking deadbolts on your closet door and that will do it.