This paper investigates the involvement of preschoolers in the late stages of the design of Child Orchestra, a musical interactive playground for the kindergarten. The study presents a retrospective analysis of the design of Child Orchestra. The system was iteratively prototyped and developed following UCD methods and a design in use approach in a kindergarten over seven months. Two groups of children (N=27) participated in design and evaluation, a group of three-year-olds and a group of four-year-olds. Both groups used Child Orchestra. To evaluate the system, we integrated the analysis of children’s drawings with field observations and interviews with teachers. The design in use approach proved to be successful in eliciting preschoolers’ needs.