Objectives Mindfulness-based programs could support children with autism spectrum disorder (ASD) and their parents to cope with autism spectrum symptoms and reduce comorbid mental health problems. In this study, we aimed to explore which change processes are involved in a mindfulness-based program for children with ASD and their parents (MYmind), according to a qualitative analysis of the families' experiences. Method Fourteen children aged 9-17 years and 31 parents (18 mothers, 11 fathers, 2 caring relatives) participated in an interview 2 to 5 months after the 9-week MYmind training, about their experiences with the training, experienced changes, and how mindfulness works for them. We used constructivist grounded theory methodology to develop a theory of the key change processes and their relations. Results Eight main change processes resulted from the analysis, namely connecting with peers, pausing, being aware, being in the here and now, letting be, determining a strategy, being and responding calm, and attuning to others. We proposed a model reflecting the interdependency and direction of these change processes. Conclusion The findings deepen our understanding of how multiple change processes are involved in the MYmind program for children with ASD and their parents. Theoretical and research implications are discussed.