In toddlerhood, parents play a crucial role in supporting the socio-emotional development of children through their parenting behaviors. Certain parental risk factors, such as emotion regulation difficulties and parenting stress, have been found to be related to both parenting practices and child outcomes. As the interplay between these risk factors and their associations with child socio-emotional problems can change across toddlerhood, the aim of this study was to investigate the longitudinal, bidirectional associations of parenting stress and maternal emotion regulation difficulties with child socio-emotional problems. This study included 360 mothers from the Southern regions of the Netherlands (M[subscript age] = 31.4, 90.7% Dutch, 81.4% completed university) who completed questionnaires biannually (Jan 2021-May 2024) within the first 3 years postpartum, as part of a longitudinal birth cohort. Cross-lagged path analyses indicated a bidirectional relation between maternal emotion regulation difficulties and socio-emotional problems over time, and a unidirectional relation between early child problems and later parenting stress. The findings illustrate how parents and children can influence each other's emotional well-being in toddlerhood.