Could computational thinking be a strong tool for children to understand complex 21st-century issues? Our knowledge is limited since most designs focus on sequential programming and on the cognitive aspects of computational thinking. This paper discusses a design that integrates ill-structured socio-scientific issues with programming and other computational concepts, in a playful and meaningful context. The design, called ChoiCo (Choices with Consequences), builds on the idea of "integrated affordances" that enables layered computational access, allowing children to be players and designers of choice-driven simulation games. We elaborate on a design-based research that studied children's activity, who progressively played, modified and co-created games that simulated real-world issues. We describe four strategies developed by the children to make sense of the simulated problems through a systems thinking approach. We also discuss how they formulated these strategies by utilizing the affordances of map design, data manipulation and coding.