Interesting thread. DS who will be 4 in June does some cool art, cut and paste and playdoh rather than drawing or painting. Part of it is he can spend an hour or more on one picture, so it becomes filled and complex. His pictures always tell a story. He extends over the edges of his piece of paper when necessary, adding pieces. Overall it looks really neat but some of it's essence is going to go away I'm sure as he learns what size drawing will fit comfortably on a page, etc. One thing he did recently had eyes both on the front and back of the paper (because animals have more than one side). But that will vanish probably the more he doesn't see anyone else put features on the back of the paper. I was kind of disappointed to see the sun make an appearance recently.
I wish he wouldn't have to be exposed to kindergarteners and first graders ever, so that he doesn't realize about the sun-house-person subject matter. Even not seeing it there he probably will get it from books etc, the cultural norms of composition.
My hope was perhaps he gets comfortable enough with his own style by doing it a lot at this young age, that down the road he won't feel so influenced by external stuff. I don't know though, it sounds like ultramarina your dd has "converted" even though she was pretty individualistic at a younger age?
Polly