1111 - it sounds like your kids are both quite gifted but in different ways (one more linear, so to speak, and one with a more imaginative, curvy path) You're going to be so busy!!
My younger sibling and I lived in our games so much. I can still remember so many of the character's names and where they lived and their family structure. Sometimes the ideas started from a book and took off on a divergent path, sometimes they were just completely original. My older sibling was not so much but she'd pop out of her books and into our game every once in a while to offer a detail or two, or more advanced vocabulary.
