The PS3 doesn't have many console exclusive young persons games - most of the games skewed towards a younger audience are multi-console so you'll find them on the Wii as well as the PS3.
They do have Little Big Planet, Ratchet & Clank, Buzz - the quiz game, and Singstar, which is not only great for kids, but drunken parent parties as well
This might change with the PS3 Move - Sony's answer to the Wiimote device - but that's not due out to later this year.
I find the best thing about the PS3 is it's media streaming capabilities. I spend more time watching downloaded videos and playing music than actually playing games on it.