This thesis is an investigation of software development for children aged six to ten years old. This is a challenging area; despite the trend for children to be exposed to computer technology at an earlier age, they often struggle to utilize it effectively. Children are not merely miniature adults; they have their own needs which are often not met by traditional software. In particular, this thesis focuses on the task of music management: a task that children take much interest in but for which they are given few tools. We address this with the design of a new music management system: the Kid's Music Box. The development of Kid's Music Box is documented in four main parts: background research, requirements gathering, design and implementation, and evaluation. Background research identifies the strengths and weaknesses of conventional music organizers with respect to young users. Requirements gathering took the form of a focus group study, which aimed to overcome the distinct challenges of obtaining input from children. The design of Kid's Music Box builds on this work, by incorporating functionality, metaphors and design elements that suit the needs and capabilities of young children. Expert evaluations and formal evaluation from children users showed promising results, which concluded that Kid's Music Box is better than other organizers in terms of managing music for children.