little big planet is a game for kids ))
Well in ways you are right, and in ways you are not…
The Story for booth games is pretty kiddy.
But the game was designed for three things: Playing other peoples levels, creating levels, and sharing levels online. So basically it is up to the community to decide weather or not the game is childish. You just cant have intense gore, and swearing… But just because you cant do gore and swearing doesn't mean it is for kids… Look at Ratchet and Clank.
And as Hennamann99 said; the game is tough, you need to be good at Mathematics, and basically solving problems using the Logic Tools provided, which is quite a challenge. I would say that if you wanted to make decent stuff on LBP you would have to dedicate around 1 or 2 months to mastering the tools you are given in create mode, but to do this you would need to be reasonably smart (Maybe around the age of at least 13)
And as much as it looks like it was designed for kids, I have noticed that all the people who are somebody's in the community are around the age of 20, because as I said, it's hard to make good original levels.