Objective The objective of this cross-sectional study was to identify related factors to obesity in children aged 7–9 years at the Demonstration School, Khon Kaen University.

Methods 268 randomly selected students aged 7–9 years from Demonstration School, Khon Kaen University, were recruited. Body weight, height and waist circumference of all volunteer students were measured to assess childhood obesity. Questionnaires regarding subjects’ demographic and environmental data were completed by their parents in order to examine related factors of childhood obesity. Data were analysed using multiple logistic regression.

Results The highest prevalence of obesity was 18% (95% CI 10.2 to 25.4) in children aged 7 years. Results from the variable screening analysis showed that the body mass index (BMI) of the father, the BMI of the mother, the habits of the father in eating fast food, drinking soft drinks and cigarette smoking, the habits of children in eating fast food and a lack of exercise by the mother were important factors. With this analysis, the significant related factors to childhood obesity were the BMI of the father (odds ratio (OR) –1.14; 95% CI 1.03 to 1.27, p = 0.012) and the BMI of the mother (OR –1.12; 95% CI 1.02 to 1.24, p = 0.021). However, multivariable analysis showed no significant related factors to childhood obesity.

Conclusion The BMI of the father and the BMI of the mother are related to obesity in children aged 7–9 years at Demonstration School, Khon Kaen University.