Ah yes, but the MK IV is WAY easier to take apart and put back together!!!
I also like the Single Six or Ruger Wrangler for what you are doing. A single action revolver is much more deliberate in its operation and in my opinion safer for first timers.
I really like a single action revolver for teaching kids because they have to pay more attention to their grip etc. since they have to cock it every time. Makes them focus on the process more. My son isn't big on pistols or revolvers (he's a rifle kind of kid) but the one time he did shoot his grandpa's Buckmark he burned through way too much ammunition in a very short time period. I had to constantly remind him to slow down and think about what he was doing. His .22 rifle is a bolt action.
Ruger mkIV is the way! I learned on an old Ruger 22lr revolver. I remember it being really fun too. I would think the revolver would be more reliable in the fact that if you have a dud, you just wait a bit, then pull the trigger again. With the pistol, you wait, then clear the round... More steps I guess.
If you have, or plan on getting, a suppressor the mkIV is the bees knee's! And it's easy to break down (like mentioned previously) to clean.
Good for them to learn good pistol skills like clearing jams and other items. Sets them up well for carrying a weapon when they get older. My experience with the single six is it is very inaccurate, compared to a Buckmark.
The Walther PK22 (CA) is nice when you're feeding it the right ammo. CCI Mini-mags work great in it. And in general the hotter stuff. Some bulk ammo I had though.. the ridges on the bullets sides, it's almost like maybe they had some oxidation or something which caused them to be extra wide in diameter ever so slightly and sometimes they'd failed to eject, to get pulled back out by the extractor claw. But clean and switch over to the Mini-Mags and she was actually a fun date to take to the range. Sights are respectable and get your kid used to 3-Dot combat sights. The trigger is neat because first pull is double action, then subsequent are single action. That part I like! We put the "shooting gallery" target up and I have him call out what he's trying to hit. The piggy's eye, or ear? The rabbits eye or butt? The hole in the center of the "O" 's in the word "Shooting Gallery" printed on the target.
A double action revolver would be best though as a very first handgun to introduce them to. Slows em down. It's like Dirt Bikes, gotta learn to walk before you can run, gotta go up tru the sizes in stages. Double-Actions adds a little more safety too since they are much less inclined to pull the trigger double-action style. And prefer to click it back single-action for the nice crisp trigger pull. The extra weight gives em confidence too since eats up what little recoil there is. And that weight out at arms length over time will strengthen them up too. Builds up their resistance to recoil when they advance to their beginning centerfire caliber like a .38 spl.
Didn't see how old the kids are but I would really push a single action vs a auto loader, even with new shooters that are adults. Takes time to familiarize oneself with firearms and a single shot is a whole lot safer. ( I know that a single action isn't a single shot)
I am a big fan of my Taurus TX22. I never thought I would own a Taurus but it has been a great shooting handgun for me. My buddy has a Ruger Mark 4 and it has only been a problem for him. He traded it in for a Taurus and has been happy ever since.
I like the above posters idea of using a single action to teach with!
I have a Browning and think I'd spend a bit more on the Ruger Mark next time, or one of the 1911 models (so light). Otherwise I'd do a double action revolver. Never cared for the single actions but folks seem to have fun with them.