DS has been carrying around a "Question and Answer Encyclopedia" book by DP Press for a few weeks. He is really into it. It has lots of pictures, but good explanations of questions like how the heart works, how the pyramids were built, why boats float, etc. I'd like to find some other GOOD books of this type. Do not suggest DK or I will whack you with a wet noodle.

(Sorry. I just don't like DK. No real narrative, poorly edited, and the content is often not well explained, interesting, or age appropriate. This book is just a lot better than DK.)
We already have The Way Things Work, or whatever that's called.