Are you speaking hypothetically or are you talking about yourself? Do you have a young child? If so, how old is he/she? What kinds of things do you observe him/her doing by his/her own inclination.
If the youngster in question is very young I can see it might be hard to translate his/her activities into specifics. But on the other hand it might not be as hard as you think. If you are speaking hypothetically, would you mind making up some specifics.
For example you might say something like: Suzy is two years old and is always making up a new imaginary friend every week, with whom she has long conversations with. Something like that -- I might say we're looking at a future actress or novelist or something like that.