My kids love this book. It's called "The Biggest Sandwich Ever." For some reason, they have both been really drawn to it. They both have gone through phases where they want it read to them each night (the youngest one is still in this phase). They've heard it so many times that they've started memorizing it. Here's Ferg's "reading" of the book from December of last year.
Now the Hanburger has started memorizing it. Here's her "reading."
If nothing else, it just goes to show you what kids are capable of. My kids certainly aren't geniuses, nor are they particular adept at memorization. But if they hear or see something enough, they will pick up on it (scripture memorization, anyone?).