Dolphin, Fox, Hippo, Ox by Brian Cleary (Lerner Publishing, 2012) and other books in the Words are CATegorical. These books are clever. Using fun rhymes, they teach about concepts that children are still learning about: parts of speech, mathematical concepts, or, in this case, animal groups.
Dolphin et al is about mammals. I liked this book enough to seek out others in the series to enjoy with my young son. In general, though, I don’t think they actually teach much. They are not nonfiction enough to cement the concepts. They provide a nice and fun introduction, however. Digital review copy.