Although 49% of Australian residents have at least one overseas-born parent, little is known about children's longitudinal bodyweight transitions among the migrant population. This study examines the net associations between maternal region-of-birth and children's longitudinal bodyweight transitions between underweight, normal, and overweight/obese status from ages 2 to 17 years. A sample of 8889 children was drawn from seven waves of a national population-based cohort study, the Longitudinal Study of Australian Children, conducted between 2004 and 2016. A multistate approach was used to investigate (i) the net effect of mother's region-of-birth on children's bodyweight transitions, (ii) the net estimation of cumulative transition probabilities, and (ii) the net conditional bodyweight expectancy, controlling for child-, family-, and neighbourhood-factors associated with children's bodyweight. Our results showed children of Oceania and African mothers had unfavourable outcomes (i.e., lower remission from or higher incidence of underweight or overweight/obese status) than children of non-migrants. Toddlers with suboptimal bodyweight status (especially those from disadvantaged groups) had higher net cumulative probabilities of staying in that status as a 17-year-old adolescent unless they managed to transfer to normal weight in the primary school years. The 15-year bodyweight expectancy depended on the initial bodyweight status at age two years, with some children of migrant mothers affected longer by suboptimal bodyweight status. In Australia, region-of-birth related disparities in bodyweight started early and were of significant duration throughout development until late adolescence. Culturally tailored health programs should begin at least as early as two years of age.