In emergency contexts such as the COVID-19 pandemic, mental health risk factors affect children and may affect behavioral and emotional problems including anxiety, self-blame, emotional disturbance, and stress. Preventive measures are crucial to address these health risks. Research highlights strength-based factors, such as socio-emotional skills and prosocial behaviors, as important for childhood development and socio-emotional wellbeing. Yet, the initial evidence base shows mixed effectiveness and insufficient behavior change theory application into socio-emotional and prosocial digital game interventions. Additionally, few interventions are designed with a clear process to convert theory into practical game solutions and very limited guidance on the digital game development process exists. This study describes the Intervention Mapping Protocol (IMP) and theory application in the design of a digital game intervention which aims to strengthen social-emotional skills development and promote prosocial behavior in 8–11-year-old children. The method systematically describes the steps of the IMP process in detail to guide future theory-based game design. The results explain the final digital game prototype that was co-designed with continuous input and insights provided by stakeholders and feedback from children. This paper contributes to our understanding of theory application in the design of digital game interventions focused on health and behavior change and provides much needed guidance on how theory and stakeholder input can be incorporated into a final game design.