People like to play, and robotic technology offersthe opportunity to interact with artifacts in new ways. Robots co-existing with humans in domestic and public environments are expected to behave as companions, also engaging in playful interaction. If a robot is small, we foresee that people will want to be able to pick it up and express their intentions playfully by hugging, shaking and moving it around in various ways. Such robots will need to recognize these gestures -- which we call "full-body gestures" because they affect the robot’s full body. Inertial sensors inside the robot could be used to detect these gestures, in order to avoid having to rely on external sensors in the environment. However, it is not obvious which gestures typically occur during play, and which of these can be reliably detected. We therefore investigate full-body gesture recognition using Sponge Robot, a small humanoid robot equipped with inertial sensors and designed for playful human-robot interaction.