The FitKids study is a mother-child observational cohort study on obesity and metabolism in children three years of age. The study will follow up on the FitMum and FitBaby studies, conducted from 2018-2022. The children in FitKids are born by mothers who completed the FitMum study, a single-site three-armed RCT, targeting physical activity during pregnancy. 220 pregnant women were randomly assigned to one of three arms during pregnancy: structured supervised exercise training, motivational counselling supported by health technology, or a control group receiving standard treatment. From inclusion and until one-year post-partum, the women wore an activity tracker 24/7 providing important information about adherence to the prescribed intervention. The primary objective of the FitKids study is to investigate the effect of lifestyle interventions during pregnancy on body composition (fat percentage measured by dual energy x-ray absorptiometry) and risk of childhood obesity in off-springs. The secondary objectives are to investigate the effect of lifestyle interventions during pregnancy on obesity-associated dys-metabolic traits and mental health in off-springs as well as to gain insight into presumed causal factors for overweight and obesity in children. The investigators hypothesize that children of mothers, who during their participation in FitMum, received an intervention will have a healthier body composition expressed as a fat percentage within the normal range for a 3-year-old child compared to children of mothers in the control group.