Most evidence of the association between maternal depression and children's development is limited by being cross-sectional. To date, few studies have modelled trajectories of maternal depressive symptoms from pregnancy through the early postpartum years and examined their association with social emotional and behavior functioning in preschool children. The objectives of this study were to: 1) identify distinct groups of women defined by their trajectories of depressive symptoms across four time points from mid-pregnancy to one year postpartum; and 2) examine the associations between these trajectories and child internalizing and externalizing behaviors.We analyzed data from the All Our Families (AOF) study, a large, population based pregnancy cohort of mother-child dyads in Alberta, Canada. The AOF study is an ongoing pregnancy cohort study designed to investigate relationships between the prenatal and early life period and outcomes for children and mothers. Maternal depressive symptoms were assessed using the Edinburgh Postnatal Depression Scale. Children's behavioral functioning at age 3 was assessed using the Behavior Scales developed for the Canadian National Longitudinal Survey of Children and Youth. Longitudinal latent class analysis was conducted to identify trajectories of women's depressive symptoms across four time points from pregnancy to 1 year postpartum. We used multivariable logistic regression to assess the relationship between trajectories of maternal depressive symptoms and children's behavior, while adjusting for other significant maternal, child and psychosocial factors.1983 participants met eligibility criteria. We identified four distinct trajectories of maternal depressive symptoms: low level (64.7%); early postpartum (10.9%); subclinical (18.8%); and persistent high (5.6%). In multivariable models, the proportion of children with elevated behavior symptoms was highest for children whose mothers had persistent high depressive symptoms, followed by mothers with moderate symptoms (early postpartum and subclinical trajectories) and lowest for minimal symptoms. After accounting for demographic, child and psychosocial factors, the relationships between depression trajectories and child hyperactivity/inattention, physical aggression (subclinical trajectory only) and separation anxiety symptoms remained significant.These findings suggest both externalizing and internalizing children's behaviors are associated with prolonged maternal depressive symptoms. There is a good case for the need to move beyond overly simplistic clinical cutoff approaches of depressed/not depressed in screening for perinatal depression. Women with elevated depressive symptoms at clinical and subclinical levels need to be identified, provided with evidence-based treatment, and monitored with repeat screening to improve maternal mental health outcomes and reduce the risk of associated negative outcomes on children's early social-emotional and behavior development.