Non-verbal synchrony (NVS) is the result of individuals aligning their non-verbal behavior during interaction. Previous research has shown a positive connection between NVS and positive aspects of human interaction and relationships. Motion-Energy-Analysis (MEA) is a method that automates and objectively evaluates NVS in situ by detecting changes in body movements from video recordings and representing them as frame-by-frame time series data. While there has been promising research on NVS using MEA in adult populations, such as couples or therapy sessions, research on parent-child-interaction (PCI) is scarce. However, given that the quality of PCI is vital for child development, examining PCI is a highly relevant topic, especially in children with a mental health condition, as they often encounter challenging and dysfunctional social interactions in their everyday lives. To close this research gap, we developed a novel lab-based social interaction paradigm comprising standardized play situations in combination with MEA to investigate NVS in authentic PCI situations. In a first pilot study, our results confirmed the feasibility of our novel paradigm and the suitability of MEA for the study of PCI. Building on this foundation, we initiated data collection in a clinical sample of parent-child-dyads (currently in treatment at our psychotherapeutic outpatient clinic) to investigate NVS between parents and their children in three different play situations. Additionally, we employ questionnaires to gather self-report information on experienced emotions, interaction quality, and relationship factors known to be linked with or affecting NVS, as well as game-related aspects to further validate our novel experimental approach.