Well, there's always Fallout and Fallout - New Vegas, which are in the same vein as Oblivion as far as character creation. Just set in an aftermath world, instead of fantasy.
Hrm, I'm trying to remember what Vampire:The Masquerade - Bloodlines was rated. Might have been M or T. If you look into that one, be sure and patch it with official and community patches though. Great game, just needs some work to get there.
Knights of the Old Republic 1 and 2 (2 had some ending issues, but if your daughters never get to the end, it won't be an issue)
Jade Empire is along the same type as Knights, just chinese mythology instead of Star Wars.
Have you thought about some of the free to play mmo's? As long as you don't let them get into the cash shop (which isn't really needed until higher levels, generally), then they can make characters all day long in those games. Some of them, like Runes of Magic and Perfect World International, have quite a bit of character customization. And since they are free to download/free to play, cheap is good