Pediatric diabetes type 1 diabetes mellitus (T1D), as a chronic, incurable disease, is associated with psychoemotional and socioeconomic burden for the whole family. Disease outcomes are determined by the metabolic compensation of diabetes, characterized by the level of glycated hemoglobin (HbA1c). The caregivers play a critical role in the metabolic control of children with T1D. The aim of this study was to investigate which environmental factors may explain the relationship between diabetes compensation and anxiety and depression of a child. The cross-sectional interdisciplinary study recruited dyads from adolescents and their parents (N = 251). Adolescent and parent groups were screened for anxiety and depression. General linear model (GLM) mediation analysis was performed to determine the potential mediating effect of surrounding factors on the relationship between dependent variables (glycated hemoglobin) and independent variables (the child's anxiety and depression symptoms). The study revealed that the relationship between HbA1c and the child's anxiety and depression is fully mediated (B = 0.366, z = 4.31, p < 0.001) by parental anxiety. Diabetes metabolic control in adolescents with T1D is related to adolescents' mental health via parents' anxiety. This means that parents' anxiety plays a more significant role in the level of HbA1c than the anxiety and depression of the adolescent.