I'd love them to keep it as children's book. It's supposed to be a story that Bilbo has written based on his adventure which he called, 'There and Back Again'. I'd start off with maybe Sam reading to a group of Hobbit children or his own little Goldielocks.
But I reckon it will be probably be dark, epic and padded out with events that are mentioned in Unfinished Tales and Gandalf's narrative to Frodo about the ring.