My daughter loves dolphins. Hers is a multi-year fascination that appears to know no end. Marty Crisp's book Everything Dolphin is a treasure trove of information that truly lives up to its subtitle, "What kids really want to know about dolphins."
It answers many of the questions a kid will have about these beautiful marine mammals--everything from "How many teeth do dolphins have?," to "Can people ride dolphins?" This book feeds her curiosity and gives us a lot to discuss. The images are lovely. Even though the reading level is above her age, my 6 year old spends ages thumbing through the book when I'm too busy to read it to her.
If your kid is fascinated by these beautiful co-habitants of the Earth, you can't miss with this book.