Mechanisms linking family socioeconomic status to children’s depressive symptoms: a longitudinal moderated mediation analysis

Background Family socioeconomic status (SES) is a well-established determinant of children’s mental health, yet the mechanisms linking SES to depressive symptoms in primary school children remain insufficiently understood. This study aimed to investigate whether loneliness, perceived social support, and parent-child relationship mediate the association between family SES and depressive symptoms, and whether these pathways are moderated by sex and household registration. Methods A three-wave longitudinal survey was conducted among primary school students in Taizhou City, Zhejiang Province, China (2021–2023). Data were collected via online questionnaires completed by students and their parents. Family SES indicators (parents’ education, family economic status, and average living space per person) were assessed at baseline (T1), interpersonal experiences (loneliness, perceived social support, and parent-child relationship) at wave 2 (T2), and depressive symptoms at wave 3 (T3). Structural equation modeling was used to examine direct, mediated, and moderated effects, adjusting for relevant covariates. Results A total of 2,164 students (mean age = 9.3 ± 1.4 years, 46.5% female) who completed all three waves were included in the analysis. Higher parents’ education was directly associated with lower depressive symptoms and indirectly associated via reduced loneliness (indirect effect − 0.02, 95% CI -0.03 to -0.001; 13.2% of the total effect) and greater perceived social support (indirect effect − 0.02, 95% CI -0.03 to -0.01; 16.3%). Better family economic status was linked to fewer depressive symptoms both directly and indirectly through greater perceived social support (indirect effect − 0.01, 95% CI -0.02 to -0.001; 11.1%). Larger average living space per person was associated with lower depressive symptoms only indirectly through increased perceived social support (indirect effect − 0.01, 95% CI -0.02 to -0.002; 43.5%). Household registration moderated the indirect pathway via perceived social support: the indirect effect of family economic status was significant among urban children but not among rural children. Conclusions Family SES was associated with depressive symptoms in primary school children partly through loneliness and perceived social support, with the latter pathway contingent on household registration. These findings underscore the importance of interpersonal processes and contextual conditions in shaping socioeconomic inequalities in childhood mental health and highlight the need for context-sensitive prevention strategies.