With note in hand I utilized Academic Search Premier to find the book review resource I may have used when determining to make this purchase. Within the database, there were two sources available; Booklist and Publisher's Weekly. Neither resource has an age recommendation, usually a good indication it should not be juvenile, and it was a starred review in both (see reviews, Amazon).
I then checked WorldCat First Search (library) and WorldCat Beta to see what other libraries had this title and where it was placed in their collections. It is a popular holding for public libraries with graphic novel collections. Only two academic libraries had it and both of them, Harvard and University of California, Berkeley, were still processing the book (as are we). With no divine inspiration from either resource it was obviously time to read the book. And yes, I do realize with the time taken to research I could have easily read the book in that same time frame.
I am not as familiar with this format, as such I rely heavily on the reviews. But after reading The Squirrel Mother Stories I determined it should not be placed in the juvenile collection. If we had a YA collection (our YA books are juvenile, regular, and recreational), it would live happily there. Lacking that classification, the regular collection is best suited for this entry. Kelso's illustrations are misleadingly simplistic at first glance. After reading the book, there are definite nuances in story and illustration suited for an adult reader. The short stories range from smart to historical and accompanying illustrations are rendered in black and white, sepia tones, and muted colors. In each instance, the story and color are paired for maximum impact.