In recent years, research on mental health during the perinatal period (i.e. from pregnancy up to one year after birth) has shown great advances, focusing on how to support (expectant) parents in this critical life stage when a family is formed or extended. However, per definition the perinatal period concludes when the family is still in its nascent stages, despite increasing evidence that the familial impact of this time-period holds the potential to span beyond these early years. This editorial thereby proposes that to comprehensively understand the significance of the formative perinatal period, a longitudinal perspective investigating child and family dynamics and outcomes beyond the first postpartum year is needed. In what follows we attempt to define the concept of ‘family mental health’ and outline key research gaps, highlighting how addressing these gaps could enhance early prevention and intervention for family well-being.