I'd say it could be a role-playing game. Not nessasarily with combat or anything, but a more literal RPG; You'll choose a role and play it.
The world would be freeform, and customisable, and rules could be coded in a candy land-esque, more juvenile system, assuming we would have something like that. (That is, without numbers and with colours and such instead.) And, of coarse, it has to be bright and colourful.