Rapidly growing research on mothers’ perinatal depression, has demonstrated significant links among mothers’ depressive symptoms during pregnancy and the first year postpartum, their parenting, and multiple aspects of children’s development. This prospective longitudinal study contributes to research on mothers’ perinatal depression by examining the mechanisms by which maternal perinatal depression is associated with children’s adjustment early in development in a sample of 204 Mexican-origin adolescent mothers (Mage at Wave 1 = 16.80, SD = 1.0) and their children (58% boys). I expected that adolescent mothers’ negative parenting behaviors would mediate the associations between mothers’ perinatal depressive symptoms and three child outcomes: internalizing symptoms, externalizing behaviors, and cognitive ability. I further hypothesized that mothers’ perceived social support from their family would modify the extent to which mothers’ perinatal depressive symptoms negatively impact their parenting behaviors and their children’s developmental outcomes. Mothers reported on their own depressive symptoms, their perceived social support from their family and their children’s internalizing and externalizing problems; negative parenting was assessed using observational methods; and children’s cognitive ability was assessed using standardized developmental assessments. In this sample, adolescent mothers’ negative parenting behaviors did not significantly mediate the relations between mothers’ perinatal depression and children’s developmental outcomes. Further, perceived social support did not significantly buffer the effects of mothers’ perinatal depression on mothers’ negative parenting or children’s developmental outcomes. However, in line with hypotheses, results indicated that mothers’ prenatal depression had a wider impact on children’s adjustment outcomes than mothers’ postpartum depression, which appeared more specific to children’s internalizing problems. Discussion focuses on implications for intervention addressing adolescent mothers’ perinatal depression, as well as the need to continue to explore protective factors that have the potential to disrupt the negative intergenerational transmission of risks.