Abstract Background Child overweight including obesity (OWOB) has quadrupled globally, since 1975. It affects a third of European children and even higher rates persist among expectant parents. Parental pre-pregnancy body mass index (BMI) and health behaviours are known to influence offspring health. Thus, this study aimed to investigate the link between parental and children’s OWOB, alongside parental socio-economic and other factors. Methods This is a population-based repeated cross-sectional study utilized data from the Salut Programme in Västerbotten, Sweden, and Swedish national registers, including 5,937 of 3-year-olds and their parents. Logistic regression analyses were used to examine the association of child BMI with prenatal BMI and other factors. Further, the Relative Excess Risk due to Interaction (RERI) arising from the interplay between parent’s OWOB status in relation to their children’s OWOB was calculated. Results OWOB prevalence rates for 3-year-olds, expectant mothers, and their partners were 15.1%, 29.1%, and 53.5%, respectively. Both parent’s OWOB significantly affected children’s BMI (with strongest association for mothers). The Relative Excess Risk due to interaction (RERI) was positive for children’s OWOB if both parents were obese, showing an additive interaction effect of individual parental obesity status. The odds for a child to be OWOB was 2.88 (1.83-4.43) if both parents were obese compared to if none of them were obese. Conclusions OWOB among preschool children remain an important public health concern in Sweden. Based on the study findings, Sweden’s regional and national public health initiatives should prioritize targeting parental overweight and obesity as a key strategy to reduce the burden of OWOB among children. Furthermore, the resemblance of these results with comparable studies across the world, emphasizing the importance of initiating interventions with parents before pregnancy or even earlier. Key messages • Parental combined obesity status significantly increase the odds of childhood overweight and obesity. • The importance of initiating interventions with parents before pregnancy for better health outcomes related to child BMI.