It's a picture book and the rhymes are amusing and simple enough for young children to understand, but the factoids tell things older kids and even adults will find fascinating. (Confession: I'm a grown up and I discovered a lot of information in this book I hadn't known before.)
I can see parents and teachers reading the rhymes out loud to children, middle graders reading it themselves, and older kids - maybe even some in High School - using the book for research to use in term papers.
Eugene Ruble's illustrations are educational, too.