The early identification of ruminative processes in children and early adolescents is particularly important to prevent the development of a stable ruminative style in later stages of development. The present study first aimed at validating a child-friendly tool, Kid Rumination Interview (KRI), to be used in a sample aged 7–12 years (n = 100; 50% females). Second, we hypothesized that maternal depression, family functioning and participants’ emotion regulation skills would be associated with children’ levels of rumination. Factor analysis on KRI scores yielded two main factors: personal life-related rumination and school-related rumination. Older and female participants showed higher tendencies to ruminate about school issues compared to their younger and male counterparts. A low-to-moderate correlation emerged between school-related rumination and child/early adolescent’s emotion regulation capacities. Mothers’ depressive rumination and mothers’ depressive symptoms were positively associated with children/early adolescents’ rumination about personal life and rumination about school issues. Conversely, an adequate and positive family functioning was negatively correlated with both school-related rumination and rumination about personal life. Hierarchical regression analyses pointed to a crucial role of maternal rumination and familiar rigidity in both types of rumination. Personal life-related rumination was also specifically predicted by maternal depression and family enmeshment, whereas school-related rumination was significantly associated with children/early adolescents’ emotional control and gender. Overall, the KRI appears as a promising tool to assess rumination in children/early adolescents. Results suggests partially different pathways to specific forms of ruminative thoughts.