As technology for children becomes more mobile, social, and distributed, our design methods and techniques must evolve to better explore these new directions. This paper reports on "Layered Elaboration," a co-design technique created to support these evolving needs. .Layered Elaboration allows design teams to generate ideas through an iterative process in which each version leaves prior ideas intact while extending concepts. Layered Elaboration is a useful technique as it enables co-design to take place asynchronously and does not require much space or many resources. Our intergenerational team, including adults and children ages 7 -- 11 years old, used the technique to design both a game about history and a prototype of an instructional game about energy conservation.