Children with developmental language disorder (DLD) often struggle with theory of mind (ToM). This study explored the link between parental reflective functioning (PRF) and children’s ToM, focusing on the mediating role of parental stress (PS). A total of 80 children aged 4–7 years (40 with DLD and 40 with typical language development, TLD) and their parents were included for analysis. Assessments included the WPPSI-IV, NEPSY-II, TEC, and ELT for children and the PRFQ and PSI-SF4 for parents. Results showed that children with DLD performed similarly to their TLD peers in terms of nonverbal intelligence but faced difficulties with cognitive and affective ToM and understanding of emotional terms (UET). Parents of DLD children exhibited low interest and curiosity (PRF components) and high PS, particularly due to dysfunctional interactions and challenging behaviors. Mediation analysis revealed that low parental interest and curiosity negatively affected children’s cognitive ToM and UET through increased PS from dysfunctional interactions. These findings highlight the need for early interventions to enhance ToM in children with DLD and support parents in better understanding and interacting with their child. Such interventions can reduce parent–child stress and promote ToM development of children with DLD, aligning with bioecological models of development.