Background: Approaches to conducting research with children afford them varying degrees of participatory power. Despite children's varying roles within research, more needs to be understood about the influences of unintentional power plays and, in particular, interactions between participant and non-participants on children's participation in "in situ" research. Purpose: This paper considers the methodological and practical dimensions of research data collection "in situ," and the effect of adult-child power relations within child-centred research. Method: Participants were children involved in a wider research project across five Australian primary schools that explored how 8 to 12-year-old children conceptualised and defined the notion of wellbeing. Drawing upon researcher observation and children's commentary and actions, a reflexive approach exploring the effects of unintentional power plays during the research activities was utilised. Data were analysed qualitatively, using a hermeneutic frame. Findings and conclusions: Three case study vignettes from the data are presented and the effect on the researcher-child relationship in each instance is discussed. Analyses of these cases offer insights into the unintentional power plays experienced by many researchers who engage in research that includes children in the naturalistic but institutionalised setting of a school. Managing effects from non-participant adults during research represents a critical ethical consideration for researchers seeking to afford children a forum to freely express their perspectives within school environments.