Learning to code, and more broadly, learning about computer science is a growing field of activity and research. Under the label of computational thinking, computational concepts are increasingly used as cognitive tools in many subject areas, beyond computer science. Using playful approaches and gamification to motivate educational activities, and to encourage exploratory learning is not a new idea since play has been involved in the learning of computational concepts by children from the very start. There is a tension however, between learning activities and opportunities that are completely open and playful, and learning activities that are structured enough to be easily replicable among contexts, countries and classrooms. This paper describes the conception, refinement, design and evaluation of a set of playful computational activities for classrooms or code clubs, that balance the benefits of playfulness with sufficient rigor and structure to enable robust replication.