Adventures in Cartooning by James Sturm, Andrew Arnold, and Alexis Frederick-Frost
Kids enjoy this book for it's humorous story of a knight and horse on a mission to fight a dragon. As they read, they're also getting a solid introduction to comic book terminology and storytelling structure. From the role of panels and dialogue to plot structure, all of these basics of comic design are explained as a part of the story. The art style is very simple, making it easy to replicate as kids are wont to do. This also encourages those who aren't confident in their drawing ability to try anyway. there are actually 4 Adventures in Cartooning books (How to Turn Your Doodles Into Comics, Activity Book, Christmas Special, and Characters in Action) as well as a recently released picture book.