Like for their twin parents, there are many fascinating family relationships for the children of twins–when identical twins have children, their children are cousins but genetically as similar as half-siblings. The Children of Twins (CoT) study examines psychopathology, psychosocial functioning, neurocognitive functioning, and brain structure and functioning in a sample of 176 substance-naïve children of twin parents from the Minnesota Center for Twin and Family Research (MCTFR) with and without a history of problematic substance use. We are also in the process of completing a neuroimaging assessment with the twin parents of children in the CoT study, which will yield the first (to our knowledge) comparable imaging assessment in twin parents and their children and will allow us to examine whether brain deviations associated with problematic substance use in adults are also observable in their young children prior to substance initiation.