My 5yo and 11yo girls have one. We just have a few games for them. My 5yo doesn't even use the 3D function and it should be used by young kids. It says right on the box that it's not for kids under 7 and kids 7-12 should only use it for like an hour at a time or it will screw their eyes up. Even my 11yo opts to not use it most of the time. Her head starts to hurt after awhile.
My older son's birthday today so we got him Madden (football) for the 3ds but he'll have to borrow one of his sisters' units (he only has a DSi XL). I'm not sure what else they have. Most of the games seem geared towards older kids. We have Bust a move (bubble busting), Nintendogs and Rayman.