For toddlers, play functions not only as a source of amusement, but also as a way for them to learn more about themselves and the world around them. Children at this age-approximately one to three years-engage in what developmental psychologist Jean Piaget called "practice play," which consists of repeated patterns of movement or sound. Through repetition, toddlers improve their motor skills and gain a greater understanding of simple cause-and-effect relationships. They might learn, for instance, that when they hit the keys of a piano, the keys will make noise, and that this same outcome will happen every time they hit the keys. Toddlers therefore gravitate towards toys with sensory appeal and a repetitive nature, such as this rolly-doll which, when tipped, will return to the upright position without fail.