My almost 4 year old son loves this book! We read it every day; sometimes 2, 3, or 4 times. At first he didn't understand the "lesson". But, after a few times reading it, he did grasp the concept of saying "please". He has told me, several times, that this is his favorite book.
A brief summary of the book: Alfie loves cookies and wants one of the cookies Mommy just baked. Using several "creative" methods, Alfie tries unsuccessfully to get a the cookies. Then, with Mommy's help, he learns the best (easiest?) way of all to get to the cookies is to say "Please").
Cute, colorful pictures, simple wording, easy concept to understand (even for a 3 and a half year old.