Summary Background Evidence regarding the association between gestational vitamin D status and offspring body composition during childhood is inconsistent. Therefore, we aimed to determine the association between maternal vitamin D and offspring lean and fat mass in the Vitamin D in Pregnancy birth cohort. Methods Subjects were mother–child pairs recruited from the Australian‐based Vitamin D in Pregnancy cohort study. Mothers were recruited before 16 weeks' gestation and provided a blood sample at both recruitment and at 28–32 weeks' gestation. Serum vitamin D 25(OH)D was measured by radioimmunoassay (Tyne and Wear, UK). Offspring lean and fat mass were quantified by using dual‐energy X‐ray absorptiometry (GE Lunar Prodigy, Madison, WI, USA) at 11 years of age. Results Median maternal 25(OH)D levels were 55.9 (42.2–73.3) and 56.1 (43.6–73.9) at recruitment and 28–32 weeks' gestation, respectively. Maternal smoking was identified as an effect modifier in the association between maternal vitamin D status at recruitment and offspring body composition. In smokers, but not non‐smokers, serum 25(OH)D status at recruitment was negatively associated with offspring fat mass percentage and positively associated with lean mass (both p < 0.05). There was no association with 25(OH)D status at 28–32 weeks' gestation. Conclusions Maternal vitamin D status in early pregnancy, in smokers, is associated with offspring body composition. These important findings warrant confirmation in larger studies and trials.