This study compared the foot morphology of Spanish schoolchildren based on their body mass index and age and analyzed whether body mass index affects the child's foot development at primary school. Cross-sectional study of 1,032 schoolchildren (497 boys and 535 girls), 6-12 years old. Height and weight were measured to calculate body mass index. Children were classified as obese, overweight, and normal-weight. Measurements of foot morphology were obtained with a three-dimensional feet digitizer in static standing. Significant differences were found between the feet of children with normal-weight and overweight (2.6 to 9.0 %) and among children with normal-weight and obese for all variables (3.9 to 17.3 %). Differences in width, ball height, and arch height (5.3 to 7.6 %) were only found among overweight and obese children. There were no changes in the foot morphology of children between 6 and 7 years and between 10 and 12 years. Obese children showed more gradual changes in the foot measurements. The average percentage increase by year in children with normal-weight and obese were similar (3.6 and 3.4 %, respectively); however, morphological measurements of the foot of overweight children increased at a faster rate (4.0 %). CONCLUSIONS Excess weight affects the foot structure of children. The differences between age groups seem to indicate that the feet of children with overweight and obesity follow a different growth pattern than that of normal-weight children. With these results, the shoe manufacturers can design shoes for children depending on their age and weight.