My youngest daughter (age 3 1/2) picked out this book at our library, and I read it not expecting to like it, but I was pleasantly surprised at how sweet the story and illustrations are. At the beginning, little rhino is an adorable agreeable child - until he learns the word "No!" and uses it all the time! Until he starts to notice he's missing out on things (surprises, playing with other children, etc). When his dad comes to pick him up from kindergarten and asks if little rhino has had a good day, he naturally says no. BUT when his dad asks him if he wants a hug, he thinks for a moment and says "Yes!" and then from then on it's his new favorite word. :)
*Review of the German edition, titled "Robert sagt Nein!"