We present a game for children, developed to inform children about global warming. The main focus is the evaluation of children's user experience with easy to use methods. We show how a field usability study including a questionnaire addressing user experience can be used, to enhance game design. The goal was to evaluate whether the game is fun or not, and what kind of improvements would increase the positive user experience of children. Categories and Subject Descriptors K. .3.2 Computer and Information Science Education General Terms Human Factors. Keywords Game, education, evaluation, children, global warming.