This trailer is a great intro:

Here are particular things I really dig about it:

- The subject matter is prime kid-bait. This book will give them many ways to think about how big a million, trillion, etc really is. It starts small with grokkable quantities (ladder rungs, cutting a cube into 1000 little cubes) and the thread of making really big numbers concrete runs through the entire book. It does this with distances (a million people joining hands would stretch from Providence to Chicago), volumes (100 billion basketballs would fill New York City roughly to the height of a person), and arrangements (between 5 and 6 trillion 9-letter "words"), among other constructs.
- The bright, humorous, borderline-psychedelic illustrations.
- The conversational and non-threatening invitations to think about mathematics that go past the words on the page. "There are about 20,000 ways to color a tic-tac-toe board with three colors." (following page) "You know, when I said that there are about 20,000 patterns like this, I was hoping that you would try to figure out exactly how many patterns there are." There are many such pages that set up tantalizing problems, that could launch some great explorations and conversations, particularly in combinatorics, geometric sequences, and graph theory.
- It introduces concepts and notation only as needed. Exponents come up organically, as do special names for them. (As a kid, I would have been particularly tickled to learn names for powers of ten past a decillion. I was a weird little nerd, but still.)
- It invites kids to read as far as makes sense to them. Schwartz compares reading the book to a game of bucking bronco: hold on as long as you can, and when you get thrown off, come back any time. You might pick the book up for your third grader, and the concept of exponents (about 1/3 of the way through) might stretch her mind. But the ideas and problems beyond could entertain and challenge her if she picks it up again in middle school and then high school.

I can't wait until my nieces come at me with "Infinity!" for the first time. I'll be ready for them.