Yes, I've read a few. I highly recommend Picture Writing by Anastasia Suen for anyone who wants to write children's books for any age. It is basically like a writing course in the form of a book.
The Children's Writer's and Illustrator's Market always has good articles in it, especially for those who are new to this business. And, of course, the most recent edition of this book is an essential tool for any children's writer who actually wants to submit their work.
Another writing book that I thoroughly enjoyed was Stephen King's On Writing (warning: his book contains some "colorful" language). It was not only an entertaining read, but he's got some great insights for the wannabe writer. Might seem strange for a children's writer to recommend his book, but there ya go. :-)