In this paper, we present a dialog system that was exhibited at the Swedish National Museum of Science and Technology. Two visitors at a time could play a collaborative card sorting game together with the robot head Furhat, where the three players discuss the solution together. The cards are shown on a touch table between the players, thus constituting a target for joint attention. We describe how the system was implemented in order to manage turn-taking and attention to users and objects in the shared physical space. We also discuss how multi-modal redundancy (from speech, card movements and head pose) is exploited to maintain meaningful discussions, given that the system has to process conversational speech from both children and adults in a noisy environment. Finally, we present an analysis of 373 interactions, where we investigate the robustness of the system, to what extent the system's attention can shape the users' turn-taking behaviour, and how the system can produce multi-modal turn-taking signals (filled pauses, facial gestures, breath and gaze) to deal with processing delays in the system.