PreS Poor Polar Bear can't find his underwear, and so, with Mouse's help, he walks off in search of his missing undies. In the well-established pattern of "That's Not My" books, the duo encounter a series of pages with die-cut underpants-shaped windows showing knickers of varying color schemes. Predictably, the undies always belong to some other animal. Each creature's skivvies reflect some characteristic of the owner. Zebra's underwear has colored stripes, Pig's has pictures of doughnuts and French fries, and Butterfly's are covered in flowers. Lively mixed-media collages illustrate the playful text. Young readers will delight in the visual gags; Squid wears a 10-legged pair of panties, and Bunny wears hers on her head. An eight-line song at the end of the book celebrates Polar Bear's underwear and asks readers, "Would you like to wear a pair, too?" VERDICT This silly import from Japan will quickly become a favorite with potty-training tots and fans of underwear humor. Rachel Anne Mencke, St. Matthew's Parish School, Pacific Palisades, CA