Interactive applications designed specifically for children offer great potential for education and play. However, to ascertain that the aims of applications are achieved, child-centred evaluations must be conducted. The design of any evaluation with children requires significant consideration of potential problems with comprehension, cognitive ability, response biases and study attrition. Multidisciplinary R&D project evaluation requirements are often extensive, requiring an all-encompassing and prolonged evaluation design. Discontinuity between the highly engaging interaction experience and the multitude of measures that form the evaluation poses a major issue for the evaluation of interactive applications. In response, we have developed Transmedia Evaluation, a method that aims to maintain engagement throughout the evaluation process. In this paper, the Transmedia Evaluation process is explained and applied to evaluate a learning application for children, MIXER (Moderating Interactions for Cross Cultural Empathic Relationships). Children aged 9-11 (N = 117) used the MIXER application and completed an evaluation battery including pre-and posttest questionnaires, immediate learning assessment and qualitative evaluation. Using Transmedia Evaluation to develop the MIXER evaluation resulted in complete data-sets (100%) for quantitative data (by self-regulated completion) along with rich, high quality qualitative responses. Transmedia Evaluation transformed the evaluation, with children fully engaging in and enjoying their experience.