Research in low-and-middle income countries links maternal depression to child undernutrition; conversely, maternal depression is a risk factor for child overweight in higher income settings. Less is known about impacts of maternal mental health in dual burden contexts or the environmental and behavioral pathways linking maternal mental health to child health outcomes. Consequently, we examine the association between maternal mental health and the dual burden of undernutrition/infectious disease and overweight/obesity in children and test whether pathogenic, dietary and caregiving exposures mediate this association. Data come from 113 mothers and their 204 children, aged 2 weeks to 15 years, participating in the Healthy Families Study in Galapagos, Ecuador from July 2018 to May 2019, with mental health, anthropometry, diet and household environmental measures. Path analyses were used to test for direct and indirect effects of maternal distress on the likelihood of children experiencing the dual burden. We found that maternal distress is directly associated with a greater risk of having a child in the household with the dual burden with significant indirect paths through the emotional climate of the household and child diet quality. Maternal distress also moderated the impact of exposure to pathogens and diet quality. Our results highlight the need to understand how maternal distress may shape care practices in environments that present challenges for mothers in acquiring adequate resources and support needed to promote healthy child growth.