This paper investigates the effects of group interaction in a storytelling situation for children using two robots: a reader robot and a listener robot as a side-participant. We developed a storytelling system that consists of a reader robot, a listener robot, a display, a gaze model, a depth sensor, and a human operator who responds and provides easily understandable answers to the children’s questions. We experimentally investigated the effects of using a listener robot and either one or two children during (...) a storytelling situation on the children’s preferences and their speech activities. Our experimental results showed that the children preferred storytelling with the listener robot. Although two children obviously produced more speech than one child, the listener robot discouraged the children’s speech regardless of whether one or two were listening. (shrink)