Four computer games were developed for children approximately from eight to twelve years of age. Different from most computer games that appeal to their players by competition, these games require two children to fully cooperate with each other in order to solve their mutual problems. The expe ctation is that children might learn to cooperate and experience the pleasure of doing so, while enjoying the games. Games must be fun, but it is a highly difficult goal to reach. This paper addresses several issues that were considered essential to game development, as well as problems encountered and how they were solved. Furthermore, obs ervation on children playing these games revealed some unexpected and interesting questions that call for further study.