Deformities of the foot result in loss of walking function. The skeletal structure of the foot develops during childhood, and quantitative assessment of the foot is warranted. In healthy children, foot length and navicular height have been studied individually; however, the foot has not been sufficiently studied in its entirety, and the growth curve of the foot has not been clarified. In particular, the heel is an important site influencing foot biomechanics. In this study, we developed a three-dimensional (3D) foot scanner and digital footprint device to examine the foot characteristics of both children and adults. This study aimed to compare the foot characteristics of developing children with those of adults. Overall, 154 children (aged 8–10 years) and 403 adults (aged 40–89 years) were included in the study. The 3D foot scanner and digital footprint device were used for measurements. Foot length, forefoot width, foot height, navicular height, and heel width were evaluated. In particular, the ratio of each indicator to foot length was used to evaluate the characteristics of the child’s foot. The measurement indices were significantly larger in adults than in children, indicating that the indices increase as children grow, irrespective of sex. The results of the measurements and the ratios to foot length showed large individual differences between adults and children in some of the measurement indices. However, there was no difference in the heel width between children and adults. In contrast, forefoot flattening was greater in adults. Increases in foot length and heel width were found to vary greatly among individuals and those with different characteristics. While foot length and navicular height increased in adults, heel characteristics did not differ significantly between children aged 8–10 years and adults. Children appear to show foot geometries and proportions different from adults, which would have important implications for the ergonomics of children’s footwear.