Any guesses as to why?
See, what's really funny is that any of us can trot up to the fiction section upstairs on a given lunchtime and find the group - and it's pretty much always a group, sometimes huddled and reading together, sometimes with a designated read-alouder, a different assortment of kids pretty much every time - enjoying these picture books. And they don't stop and pretend to be busy and important with something else when any of us appear. They carry right on, with half an eye on us to see if we're going to react (I just grin!). I've had some, smirking, tell me these are appalling and rude books, and shoudn't be in the library. I say I'm appreciative of their input, and did they enjoy them?!
Actually, they're charming and fun and convey accurate information in a friendly and accessible format. Mummy Laid an Egg is another one in this category. I've written about them before, here: http://skerricks.blogspot.com/2009/06/gifsl-30-naughty-books-about-sex.html.
I love having books with legs in the library!
We used to have one with the immensely promising title, Boys & Girls & Sex, which started lunchtime on the nonfiction shelf in the 613s and rarely if ever ended lunchtime there. Another group read, although it was drier nonfiction, with some drawn illustrations (sadly added to so often that it was one of the reasons it had to be disposed of from the library). Its thumped condition attested to its keen readership (and they could work the catalogue and library systems well enough to find it independently, because sex isn't the first topic a kid's going to enquire about from a teacher librarian. Besides, it's a well-known fact - ask any teenager - that no teenager's parents have EVER had sex, because the thought is just too gross and embarrassing for their kids to contemplate. Immaculate conceptions, pretty much every kid in high school. Remarkable, really.) but it had rarely been borrowed. By gum it got to travel around the library though! - we'd find it tucked into all sorts of unlikely shelf locations. And reshelve it in the 613s, and wonder where we'd find it next...
Ah, the happy life of teacher librarians, enjoying the books with legs!