Here are 3 sample projects that happened in our house (after mine and the 4 year old's, I was booted off the set so the 7 year old could take over).
In the one marked "by a grown-up", they assisted and were trying to use shadows to our advantage in this one - still a work in progress! (We had a few stray pieces of play-dough in the background, but that's another great lesson to learn for next time.)
In the one marked "by a 7 year old" she really did this start to finish on her own, from characters to story to changing their expressions.
In the one marked "by a 4 year old" she ran the show and I just helped when eyes feel off and stuff like that :)
Hope you are having fun experimenting with your own ideas and can't wait to see your projects!