The COVID-19 pandemic has presented families around the world with extraordinary challenges related to physical and mental health, economic security, social support, and education. The current study capitalizes on a longitudinal, cross-national study of parenting, adolescent development, and young adult competence to document the association between personal disruption during the pandemic and reported changes in internalizing and externalizing behavior in young adults and their mothers since the pandemic began. It further investigates whether family functioning during adolescence 3 years earlier moderates this association. Data from 484 families in five countries (Italy, the Philippines, Sweden, Thailand, and the United States) reveal that higher levels of reported disruption during the pandemic are related to reported increases in internalizing and externalizing behaviors after the onset of the COVID-19 pandemic for young adults (Mage = 20) and their mothers in all five countries, with the exception of one association in Thailand. Associations between disruption during the pandemic and young adults’ and their mothers’ reported increases in internalizing and externalizing behaviors were attenuated by higher levels of youth disclosure, more supportive parenting, and lower levels of destructive adolescent-parent conflict prior to the pandemic. This work has implications for fostering parent–child relationships characterized by warmth, acceptance, trust, open communication, and constructive conflict resolution at all times given their protective effects for family resilience during times of crisis.