4-8 year olds: The Lion Day-By-Day Bible. Here's that rare thing: a kids' Bible that is both comprehensive and simply written. It retells much more of the Bible than most kids' Bibles, doesn't miss the scary bits, and actually covers the whole story of Jonah! The readings (one for each day of the year) are short and well-told, and the illustrations are gorgeous.
I won't know until I've read it to my kids, but I think this might be one of the best classic kids' Bible I've seen. If it is, it will move into top spot on my list of suggested children's Bibles alongside The Jesus Storybook Bible and The Big Picture Story Bible, which are stronger on biblical theology, but less strong on retelling as many of the Bible stories as well and simply as possible.