This paper presents a prototype learning environment for children to create their own knowledge about multivariate systems. We developed a virtual world linked to a tabletop-sized physical dome in which children experiment with envirojnmental parameters affecting plant growth. A key concern of the design was giving children control of the temporal domain, allowing for the playful exploration of cause-and-effect relationships. We show how this resulted in a tool in which children may create, exhibit and reflect upon their own knowledge by challenging and exploring their conceptions of variable interactions.