@nixCraft I don't know if updates have changed that, but Half-Life is pretty well optimized. If violence is not something the children want, then probably Portal.
Pcsx2, dolphin and ppsspp, can let you run games from other platforms quite easily. I'd probably suggest any Zelda, Medievil and Finaly Fantasy game, but if again, graphic content is not desired, then look for games like ICO.
I can't really suggest anything else, since I mostly play horror and/or games with vioent elements. Sorry.