To examine if parent illness uncertainty is indirectly associated with child depression, anxiety, and HRQOL in the CKD/SLE population. Parent–child dyads (N = 31) from outpatient rheumatology and nephrology clinics included children (ages 9–18) diagnosed with CKD (Stage 1, 2, or nephrotic syndrome) or SLE. Parents completed demographic and uncertainty measures and children completed uncertainty, depression, anxiety, and HRQOL measures. This cross-sectional study examined mediational models using the percentile bootstrapping method. Parent uncertainty had an indirect effect on child depression, anxiety, and HRQOL through the mediator, child uncertainty. In other words, parents’ illness uncertainty regarding their child’s condition correlates to the child’s illness uncertainty, which then is associated with the child’s mental health and wellbeing. Reverse mediations illustrated that parent uncertainty did not mediate child uncertainty and outcome variables. Results extend previous research by examining parent and child illness uncertainty in understudied conditions (CKD/SLE) and the relationship to outcome variables commonly related to depression (e.g., anxiety and HRQOL). Findings allow health psychologists and medical personnel to understand the impact of uncertainty on the child’s wellbeing and HRQOL. Clinical implications, including using specialized interventions to address illness uncertainty, are discussed.