Although psychopathology in mothers is known to be a significant risk factor for child outcomes, less is known about how emotion dysregulation, a transdiagnostic feature that cuts across many diagnoses, shapes emotion-related parenting practices and the development of emotion regulation in offspring. Building upon previous research that examined the functional relations between emotions and regulatory actions in children, we sought to examine the association of maternal emotion dysregulation and emotion socialization with these functional links in an at-risk community sample of mother–preschooler (children ages 36–60 months) dyads that oversampled for mothers with elevated symptoms of borderline personality disorder (n = 68). We found that maternal emotion dysregulation was associated with children displaying more sadness and engaging in less problem solving during the Locked Box Task, which is designed to elicit anger. Maternal emotion dysregulation was also associated with children being more distracted and talking less in the context of sadness. Maternal nonsupportive emotion socialization responses were associated with children engaging in more defiant behaviors throughout the task and using less problem solving in the context of happiness, whereas maternal supportive emotion socialization responses were associated with more play throughout the task and less talking in the context of sadness, above and beyond the effect of maternal emotion dysregulation. These findings indicate that maternal emotion dysregulation and nonsupportive emotion socialization practices are both meaningfully associated with the development of aberrant patterns of emotional and behavioral responding during the preschool years.