A digital musical instrument, the “Musical Playpen”, was developed in an effort to provide children with immersive musical experiences. The instrument senses children's motion inside a playpen filled with plastic balls and maps their gestures to musical output. This allows the players to use familiar and fun play activities while exploring the musical consequences of their actions. Observations of children's play patterns in the instrument suggest that immersive musical experiences can introduce infants and toddlers to a variety of creative and expressive musical experiences, rarely offered by traditional musical instruments.