This book is not for people who would prefer to not know that our bodies are home to lots of other creatures, and that those creatures make us smell, eat our dead skin, sweat, and body oils, and then leave their waste products, carcasses, and eggs littered about their ecosystem, i.e., us.
That said, it's a pretty cool book if you've got the stomach for it. The photographs are disgustingly cool, the text is very accessible to elementary school aged kids, and as a result it makes the world of microbiology and science accessible to kids, too.
Most importantly, after reading the "Zoo in Your Mouth" chapter, I'm pretty sure my niece is now finally convinced that it is important to do a very good job brushing her teeth. If this book does nothing else to educate her, then it's done its job, and it's worth it to know that I'm public transportation for a large number of God's creatures.
The downside to this book (I'm not considering the "ick" factor to be a downside--the cover alone gives you fair warning) is that it was a little too long to hold my niece's attention all the way to the end. She is seven and she did pretty well, but the book was probably just a little ahead of her level. The book includes a glossary, an index, a "further reading" list, and a referral to an internet site facthound.com
that kids can safely use to find age appropriate materials that will satisfy their curiosity on a multitude of subjects.