© 2021This paper aims to develop new co-design techniques for narrative design from scratch in the digital game design process with children. Designing from scratch requires the plain preferences of children and creativity (creative contributions) from their intrinsic drives. Therefore, it is crucial to understand and leverage “children's imagination”. To trigger children's imagination, we proposed three novel approaches to develop new co-design techniques that are based on (1) game elements, (2) narrative models, and (3) Philosophy for Children (P4C). Using these approaches, narrative design processes for digital games were performed by an intergenerational design team that included eight children aged 7–11. Children played the role of design partners in the participatory design setting. Data analysis was performed using an analysis framework with two domains: co-design process (implementation, involvement of children, and involvement of adults) and game narrative design (involvement of children and product features). The first technique, Five Elements, was based on game elements and had many strengths in game narrative design and the involvement of children and adults. There are some challenges in implementation because it requires a substantial time commitment, it is not easy to allocate adult team members, and it is difficult to arrange the environment. The second technique, Game Motif, was based on narrative models and had many strengths in all of the criteria, except variety in game genres, which is related to product features. The third technique, Superhero Enquiry, was based on P4C and had limited strengths, including the involvement of children in the co-design process and game narrative design. This paper indicates the strengths and challenges of the new techniques and presents the techniques themselves. It offers some improvements to use these approaches in more effective ways. Consequently, academia and industry can benefit greatly from the contributions of children's imagination when designing digital games for children using these new techniques appropriately in a given context.