For newbie guns, the .22 is good idea even for an adult:
1. The price is lower than other guns
2. The recoil is gentle.
3. The trajectory is flat.
4. Because of 2 and 3, it's easier to shoot accurately with a .22. Hitting what you're aiming at early in the learning process is a good thing. It provides lots of positive feedback.
5. The ammunition is inexpensive.
If a newbie buys a .22 and turns out to not like shooting, he's not out much. A decent .22 is not difficult to sell used. And the same thing applies if the newbie enjoys shooting and wants something bigger: he hasn't spent that much and can likely recover at least half of it to apply to his next gun.
And the .22LR is not a total loss as a self-defense round. The velocity is high (and you can get hollowpoints) and they make a nice loud sound. It's probably not going to stop Mongo the Man-Mountain with one shot; but the bulk of instances of defensive gun use don't involve firing even one shot. You can't do much worse than a .22 (though my little .25 Eibar-type pistol comes to mind...) but it's better than nothing.
Flip side, if you shoot .22s well, you'll shoot accurately with .38 Super, too, and that's not cheap at all. Drat!
--Herself