Serum 25-hydroxyvitamin D (25OHD) is the main circulating form of vitamin D in the blood. Vitamin D status in adults is determined by numerous factors such as oral intake, skin generation, and body composition. However, there is limited understanding regarding determinants of 25OHD in young children. The aim of this study was to identify modifiable factors that may act as determinants of 25OHD at five years of age. Analysis conducted on 79 children from the ROLO Kids study. Dietary intakes and dietary habits were measured using a food frequency questionnaire and levels of sun exposure were assessed using a lifestyle questionnaire, both completed by the mother. Child weight, height, and skinfolds were measured. Vitamin D status was sufficient (25OHD > 50 nmol/L) in 61% of the participants. Neither reported dietary vitamin D nor calcium intake was significantly associated with 25OHD. Intakes of standard milk, eggs, and oily fish were not associated with 25OHD. However, reported consumption of fortified milk, and more than 7 bowls of cereal a week were independently associated with higher 25OHD (p < 0.001 and p = 0.049, respectively). Sun exposure (measured as obtaining at least half an hour of sun per day) was not significantly associated with 25OHD, but reported use of sunscreen was associated with higher 25OHD (p = 0.016). There was no association of body composition with 25OHD. These findings suggest the primacy of dietary and lifestyle habits as indicators of 25OHD in early childhood. This may have utility in identifying at-risk individuals for public health campaigns about education surrounding dietary habits, which may be useful to ensure sufficient vitamin D status within this age group.