Goodness knows that there are a ton of penguin books out there for kids, and they are probably all remarkably similar to one another. As far as penguin books go, though, I did think that this one by Jenny Markert was quite well done.
A wide variety of species were pictured and discussed, and my niece, nephew, and I were all quite suprised by the diversity among penguin species. The text in this book was very well written, too. It was easy for the kids to understand, and the "chapters" were quite brief (1-2 pages in length). The book might have been a tiny bit long for my nephew to manage in one sitting, but he did do pretty well with it. This book might work best for younger kids if parents or teachers just read a few chapters a day. The full length is certainly digestable for older kids, though.
I dislike non-fiction children's books in which the pages are just a riot of facts, pictures, text. They seem unfocused, and there is no white space for the eye to just rest. This book does not suffer from that problem. The captioned photos of the penguins are big and bold, and the text is accompanied by a couple of additional penguin facts. Perfect avoidance of information overload without being light on the education. At different points in the book each of us remarked, "Huh! I never knew that," so I'm going to have to say that this is a good one.