Willems, Mo Big Frog Can’t Fit In. Hyperion, 2009. $19.99. Content: G. POP-UP BOOK. Big Frog is really just too big. No matter how he squirms and twist, he can’t fit within the pages of the book. With sole help from some little friends, however, there may just be a solution. Big Frog is awfully cute and so is her book. There are just so many cute pop-up (Willems call this a “pop-out”) books this season – every child you deserves one just for them. PreK – ADVISABLE. Cindy, Library-Teacher.