Pandamonium — Frank Asch

Pandamonium is book 4 in the series called Class Pets. It is the continuing tale of two mice, Jake and Molly. Jake is content to live in the walls of P.S. 42 and dine off the scraps the students leave behind from their lunches for the rest of his life. But one night Molly comes to her brother with a scheme that she's convinced will finally realize her unlikely dream of becoming a class pet. The result is a death defying adventure involving sweet first grader, Ava, a stuffed Panda Bear, and a night spent shivering in a refrigerator…