Among children in the United States, there is a high prevalence of psychopathology. Understanding what contributes to the development of these disorders in early adolescence and late childhood is key to informing intervention efforts. This study aimed to understand the impacts of economic and social stress on the development of internalizing and externalizing psychopathology in children. Additionally, with the knowledge that supportive adult relationships can buffer psychopathology impacts, it sought to uncover if supportive sibling relationships can alter the relationship between stress and psychopathology. Data was collected through both home visits and online questionnaires as part of the Arizona Twin Project. The sample of the twins at eight years old included 355 families (M = 8.43 years, SD = .68) and 709 twins (MZ = 29.9%, same-sex DZ = 37.8%, opposite-sex DZ = 31.7%, and unknown zygosity = 0.6%) with ethnically and socioeconomically diverse backgrounds. Families were followed longitudinally with annual assessments at ages 9, 10, and 11. Our results showcased a significant positive relationship between economic stress and the development of internalizing and externalizing psychopathology symptoms in children. Our social stress indicators were categorized into family stress and negative parenting constructs. It was observed that family stress was linked to an increase in both internalizing and externalizing symptoms. However, when it came to parenting behaviors, no significant associations were identified with the development of either externalizing or internalizing symptoms in our study. In terms of the potential moderating effects of a positive sibling relationship, no significant results were found. Ultimately, our study showcases the adverse impact of stress on children and early adolescents. Further research on the impacts of the relationship between siblings can help us to better understand the dynamics in the home as a whole and explore whether relationships beyond those with supportive adults can contribute to resilience in children. This knowledge may guide interventions and preventive measures aimed at mitigating the effects of psychopathology in young individuals.