This paper describes an explorative user study with interactive objects for open-ended play, i.e. play with flexible game goals and rules. Children were asked to play with interactive objects, called the ColorFlares, in three free play sessions over a period of three weeks. We measured social interaction in terms of social play and social communication. We found that group play over all three sessions remained high. We also found that communication in the first session was mainly about the

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... bilities of the ColorFlares. Later on, communication was related more to the games that were played, giving each other feedback. We also discuss the personal and situational factors that have influence on the test results.