INT. BAG END - NIGHT
Sam Gamgee settles down in his armchair to smoke his evening pipe. His children crowd around him.
ELANOR: Daddy! Tell us a story!
SAM: Would you like to hear the story about how Mister Frodo and I journeyed to Mordor to destroy the Ring?
ROSE: You always tell us that one!
GOLDILOCKS: Tell us a different story!
SAM: Well, have I ever told you the story of how Old Mister Bilbo went on an adventure and found the Ring?
HAMFAST: No you haven't.
DAISY: Tell us that one, Daddy!
Sam picks up a large red book and opens it to the first pages.
SAM: (reading) In a hole in the ground there lived a hobbit...
EXT. BAG END - MORNING
Bilbo Baggins sits on the front porch of Bag End, blowing smoke rings.
This opening scene serves multiple purposes. It ties The Hobbit in with The Lord of the Rings, establishing this as a prequel. But since it is framed as Sam telling the story to his kids, it allows for The Hobbit to be more of a children's movie. The book takes a very pro-Bilbo stance, treating the Thorin and Company as a bumbling band of misfits. If Sam were narrating the movie, it would only make sense for him to build up Bilbo as one of the most famousest of hobbits and the only one with any real amount of common sense. The narrator of The Hobbit has several good lines and making Sam the narrator would help get those lines into the movie. And it could also provide a means to address some of the inconsistencies between the books as the children could interrupt Sam's story on several occasions, much like Fred Savage does in The Princess Bride. Sam could then provide an explanation for the differences, he could essentially say, "Shut up. I'm telling a story," or he could even say, "That's how Mister Bilbo wrote it and so that's how I'm telling it," which would be a sly way of shoving the blame back on Tolkien. And I think Tolkien would approve of this approach because he was obsessed with framing narratives. Of course I would have to restrain myself from inserting a scene right after the "Tra-la-la-lally" song in which one of the kids asks, "Is this a singing book?"