The Mixed-Up Chameleon, by Eric Carle, Harpers Collins.
I love Eric Carle books; his illustrations are so completely perfect that even if the text were to falter (which it does not), the book would still be worth buying.
This book is probably Eric Carle's silliest, and therefore most fun for young readers, book. It is pretty hilarious to see the chameleon change after each animal is added.
And, without using a sledgehammer, it does have a nice message at the end of the story.