Purpose <p>Theory of mind (ToM) and everyday social interactions are inherent aspects of child development. In families with autistic children, variations in these domains may be linked to increased parental stress. However, their collective interplay remains unknown. This study investigated the potential mediating effect of everyday social interaction in the relation between ToM and parental stress.</p> Methods <p>A cross-sectional study was conducted for 91 parent–child dyads of autistic children. Participants demonstrated substantial variability in verbal comprehension (mean = 98.4, SD = 23.0, range = 45–155). Parental stress, children’s ToM, and everyday social interaction challenges were assessed. Mediation analysis with bootstrap resampling was conducted to analyse the data.</p> Results <p>After controlling for age and verbal comprehension, social interaction challenges mediated the relations between ToM and overall parental stress (effect size = -0.69, 95% CI = -2.39, -0.09) and three aspects of parental stress (effect size = -0.27 to -0.21, 95% CI = -0.82, -0.00).</p> Conclusion <p>These findings highlight the mediating role of everyday social interaction in linking ToM to parental stress, emphasizing the relevance of interventions that consider ToM development, everyday social interaction skills, and parental stress management. Facilitating the everyday social interactions of autistic children may favourably influence parent–child relationships and be associated with reduced parental stress, indirectly reflecting the positive link between ToM and children’s social functioning. Therefore, future supportive programs might simultaneously focus on ToM development and everyday social interaction skills to foster better outcomes for autistic children and their families.</p>