This study was performed to reveal factors associated with dietary supplement use among Japanese preschool children in a nationwide survey. A cross-sectional, Internet survey was conducted among 2,058 mothers aged 20-40 y old who had preschool children and were registrants of a Japanese social research company in February 2013. The questionnaires assessed dietary supplement use, lifestyle and eating habits in both children and their mothers, eating awareness among mothers and the mothers' sources of health information. The study employed logistic regression analysis to evaluate the association between dietary supplement use and other variables. Dietary supplements were used by 8.0% of the children. Children who used supplements tended to be older in age, less likely to "get up cheerfully every morning," more likely to skip breakfast, eat out more frequently, and have mothers who used supplements, than children who did not use supplements. Mothers' level of education and household income were not associated with supplement use among their children. It is likely that mothers' anxiety about their children's health or unhealthy eating habits has a striking effect on supplement use among children. However, the actual dietary balance and daily rhythms of child supplement users were not irregular or unhealthy. It is necessary to give more accurate information on children's dietary habits and health to address mothers' anxiety.