Objectives The purpose of this study was to examine the mediating effect of marital conflict and the moderated mediating effect of social support in mothers’ work-family conflict and school adjustment in children. Methods Among the data from the Panel Study on Korean Children(PSKC), the final sample consisted of 400 respondents who answered questions on work-family conflict, marital conflict, child school adjustment, and social the 8th year, when the children were in the first grade. SPSS Macro’s Model 4 was used to confirm the mediating effect of marital conflict in the relationship between mothers’ work-family conflict and school adjustment in children, and SPSS Macro’s Model 1 and 7 were used to analyze the moderating effect and moderating mediating effect of social support. Results First, mothers' work-family conflict showed a positive correlation with marital conflict and a negative correlation with social support and children's school adjustment. Marital conflict negatively correlated with social support and children's school adjustment, while social support did not show a significant correlation with children's school adjustment. Second, marital conflict mediated the relationship between mothers' work-family conflict and children's school adjustment. This means that work-family conflict directly affects school adjustment and also has an indirect effect through marital conflict. Third, in the relationship between work-family conflict and marital conflict, the group with a higher perception of social support showed a mitigating effect on marital conflict compared to the group with a lower perception of social support. Fourth, the study confirmed the presence of moderated mediating effects, indicating that the relationship between work-family conflict and children's school adjustment via marital conflict varies based on the level of social support. Conclusions Parents with children entering school may experience higher marital conflict in dual-income families than at other times, which can make it difficult for children to adapt to the new environment of school. Therefore, it suggests the need for social support and systems that can reduce work-family conflict and marital conflict experienced by the primary caregiver, as well as emotional support.