Early exposure to maternal depression is a key risk factor for child mental illness (MI), but there are limited programs that interrupt intergenerational transmission. The BRIDGE “Building Regulation in Dual Generations” Program treats maternal MI using Dialectical Behavior Therapy Skills with a paired curriculum that promotes non-reactive and emotionally validating parenting designed to improve child mental health and ultimately prevent MI. The pilot feasibility trial (n = 28 dyads) included mothers and their preschool-aged children. The 20-week program was completed in a group-based format using mixed methods questionnaires and interviews. Results indicate high feasibility and acceptability (86% retention). Consistent improvements were seen across program targets and outcomes including maternal depression (d = 1.02) and child mental health (d = 1.08), with clinically significant symptom reductions for 85% of clients. Mothers with higher adversity exhibited greater reductions in parenting stress. Qualitative results highlighted efficacy in promoting positive parent–child relationships, rewarding parenting experiences, competence, and child development. Evidence suggests high feasibility and accessibility for BRIDGE in addressing intergenerational mental health needs. There was strong satisfaction with the program material and efficacy across key outcomes. BRIDGE holds promise for offering a transdiagnostic approach to preventing child MI in families of at-risk preschool aged children.