Perseus Publishing Mommy has a surprise for Caillou: a potty for him to use. Caillou is a big boy now. Bestselling title in the Hand in Hand series! In this delightful story Mommy has a surprise for Caillou: his very own potty! Though initially uninterested, Caillou eventually decides that he wants to be a "big boy" and leave his diapers behind. After several attempts, a few failures, and near misses, Caillou learns to ask for the potty when he needs it and is rewarded with a sense of accomplishment and independence. Written with input from child psychologists, the Hand-in-Hand series of books helps children navigate their way successfully through various key developmental experiences of childhood.