This article concerns children's engagement and participation in a musical dialogue, with the adult taking the role of the more-experienced participant and frames the activity as a musical play activity (in both senses of the word "play"). It presents an analysis of empirical data from a session with two six-year-old children interacting with and around a new music technology in a Swedish preschool setting and explores what participating in these practices implies for the children's learning. The results indicate that the communicatively established framing made it possible for the children (i.e. provided scaffolding for them) to participate actively in a joint playful music-making activity. The communicative framing provided by the adult who took the role of a more-experienced participant played a vital part in providing musical experiences, not only in guiding the children to explore the system but also in introducing mediating tools as a way of discerning musical aspects.