Mired in Mud

That's what I feel like right now. Going through books and deciding what to keep and what to give away must be my kryptonite. Having five children ranging in age from 3-12 pretty much means that we're FULL of books... our shelves are at overflow. How does one decide what books to keep? How can I DO that?

I've got a great storage and display solution for them, but it means that we need to whittle down the collection.