Co-design or participatory design has emerged as a useful concept where stakeholders and end-users have a greater stake in designing the end product. To date, few accounts exist of the use of the concept in serious game design, especially for children with chronic diseases. We report initial steps in serious game co-design for children with type 1 diabetes. Participants included 14 children (mean age 8.6 years, range of 4-13) who were invited to sketch a diabetes game. The most prevalent themes that emerged from the sketches (N=17) include blood glucose monitoring (n=12), nutrition (n=8) and insulin (n=8); all of which are consistent with diabetes education guidelines. Co-design is a promising concept for understanding children's world-view when designing healthcare games.