Measuring fun and enjoyment with children is not trivial. Subjective measures are known to suffer from an experimenter effect and often lack detail in their answering. With increasing age, children develop increasing skills and ability which explain their different answering tendencies as compared to adults. Piaget noted the development of thinking skills around the age of 11, where children learned to use abstract concepts and reflect upon them. This includes selfregulation, a skill consisting of self-motivation, attention control, self-monitoring, and self-evaluation. For a subjective measure of fun and enjoyment these skills are pivotal. Special subjective instruments have been developed for children, such as the Smileyometer. This instrument uses images of smileys to make the items on a scale more recognizable. In this paper we will review the Smileyometer on the basis of two studies in a science museum in The Hague, The Netherlands. Both studies evaluate the enjoyment of children during a quest through the museum that started at a multi-touch table with the selection of topics of interest from the museum’s permanent exhibition.