A mobile robot toy must be designed to be capable of facing the variety of situations that can be experienced in a household environment, while still be appealing to children and create interesting and meaningful interactions, all at a reasonable cost. In this paper we present Roball, a rolling robot. Children are used to play with ball-shaped objects, making Roball implicitly appealing. In addition, its spherical shape allows Roball to show robustness in facing all kind of obstacles, surfaces, and interplay situations. This paper describes the robot and observations made of children playing with Roball.