<p>Kenyan adolescents experience a high burden of depression and anxiety, compounded by childhood trauma and limited access to mental health services. This study examined associations of cumulative childhood trauma exposure (ACEs) and perceived family social support with depressive and anxiety symptoms among Kenyan secondary school students. A cross‑sectional secondary analysis was conducted using data from 17,089 adolescents collected across 63 public secondary schools in Kenya. Depressive and anxiety symptoms, adverse childhood experiences, and perceived family social support were assessed in separate survey versions. Multilevel models accounting for school clustering were fitted to the respective ACE (<i>n</i> = 1,932) and family support (<i>n</i> = 2,005) subsamples. Each additional ACE was associated with 0.75‑point higher depressive symptoms and 0.82‑point higher anxiety symptoms (<i>p</i> &lt; .001), adjusting for age, gender, school form, and school clustering. Higher family social support was significantly associated with lower depressive (b = − 0.17, <i>p</i> &lt; .001) and anxiety symptoms (b = − 0.16, <i>p</i> &lt; .001). These findings indicate distinct risk and protective associations with adolescent mental health. Cumulative childhood trauma is a strong, graded correlate of adolescent depression and anxiety in Kenyan schools. Family social support appears to be a meaningful protective factor. The cross-sectional, self-report, split-survey design limits causal inference and prevented joint analysis of trauma and family support. Trauma-informed screening and family-strengthening interventions in school-linked services may benefit adolescent mental health in low-resource settings.</p>