The sketches are highly entertaining, and give the book a hint of a graphic novel feel. Although the main character is a girl, the sketches and diagrams, not to mention many of the events, feel boy-friendly, too. I think that Penguins of Doom will please boys and girls or all ages, nine and up.
Incidentally, it's no coincidence that the release date is 7/7/7. Sevens feature prominently in this book about a seventh child.