Children affected by HIV and AIDS have significantly higher rates of mental health problems than unaffected children. There is a need for research to examine how social support functions as a source of resiliency for children in high HIV-prevalence settings such as South Africa. The purpose of this research was to explore how family social support relates to depression, anxiety, and post-traumatic stress (PTS). Using the ecological model as a frame, data were drawn from a 2011 cross-sectional study of 1380 children classified as either orphaned by AIDS and/or living with an AIDS sick family member. The children were from high-poverty, high HIV-prevalent rural and urban communities in South Africa. Social support was analyzed in depth by examining the source (e.g. caregiver, sibling) and the type (e.g. emotional, instrumental, quality). These variables were entered into multiple regression analyses to estimate the most parsimonious regression models to show the relationships between social support and depression, anxiety, and PTS symptoms among the children. Siblings emerged as the most consistent source of social support on mental health. Overall caregiver and sibling support explained 13% variance in depression, 12% in anxiety, and 11% in PTS. Emotional support was the most frequent type of social support associated with mental health in all regression models, with higher levels of quality and instrumental support having the strongest relation to positive mental health outcomes. Although instrumental and quality support from siblings were related to positive mental health, unexpectedly, the higher the level of emotional support received from a sibling resulted in the child reporting more symptoms of depression, anxiety, and PTS. The opposite was true for emotional support provided via caregivers, higher levels of this support was related to lower levels of all mental health symptoms. Sex was significant in all regressions, indicating the presence of moderation.