Caillou is a four-year old boy and the main character of the program by the same name. He is 3 years old in the program's earliest episodes, but 4 in most of them. He is an inquisitive and curious boy who loves cars and dinosaurs and lives in 2 story blue house with his parents and his sister, Rosie. Later installments of the program show him attending playschool. In the earliest installments of the program, Caillou is normally seen wearing a dull grey shirt with a bright red collar, but he is later seen in a bright yellow shirt with the same red collar.