I bought this for my 12 year old nephew and couldn't resist looking at it first. I think it's an incredibly fun read, packed with mind boggling information. It also contains a lot of the stranger and even quite gruesome things that boys that age like. I would point out that for some younger children aspects of the human details may be too revolting - but then again, many kids love the idea of people with body parts that appear very "unusual," to put it mildly.
When I was a kid I always got the Guinness Book of Records, and enjoyed seeing some of the more bizarre things people will do, or have naturally about them. This book does more of the same but with many great pictures and seems to be geared around the quirkly, bizarre and outrageous. A really fun read.