Emerging themes in demography, developmental medicine, and psychiatry suggest that a comprehensive understanding of mental health across the life course requires that we incorporate the lives of children into our research. If we can learn more about the ways in which the stress process unfolds for children, we will gain important insights into the factors that influence initial set points of trajectories of mental health over the life course. This will simultaneously extend the scope of the stress process paradigm and elaborate the life course perspective on mental health. Incorporating children's lives into the sociology of mental health will also extend the intellectual influence of the discipline on sociomedical and biomedical research on mental illness. I contend that sociology's greatest promise in understanding trajectories of mental health across the life course lies in a systematic analysis of the social and social-psychological conditions of children, the stressful experiences that arise out of these conditions, and the processes that mediate and moderate the stress process in childhood. In this regard, there are three major issues that sociologists could begin to address: (1) the identification of structural and institutional factors that pattern children's exposure to stress; (2) the construction of a stress universe for children; and (3) the identification of key elements of the life course perspective that may set or alter trajectories of mental health in childhood and adolescence.