I really recommend Psychonaughts. I think you will find that it is not only appropriate for kids of all ages, but that they will absolutely get an enormous kick out of the unbelievably imaginative artwork and level design. Everything about the game, including the premise of a kid at summer camp, solving a big mystery without the help of (and even in spite of obstruction) by adults. It's similar to Harry Potter in that way, I guess. There is a very small amount of very mild language. I think that there are one or two places where someone says "ass", and it seems like it's in some kind of pun-type thing kind of like that rhyme about miss suzy having a sailboat, and behind the refrigerator there was a piece of glass, little Susy sat on it it stuck right in her . . . ask me no more questions . . .
That sort of thing. Anyway, it's extremely mild. Maybe I'm just not as protective as some, but I would let my four-year-old play that game as soon as my fourteen-year-old.