This study investigated the association between food insecurity and Taiwanese children's ambulatory medical care use for treating eighteen disease types linked to endocrine and metabolic disorders, nutrition, immunity, infections, asthma, mental health, injury, and poisoning. We used longitudinal data in the Taiwan National Health Insurance scheme (NHI) for 764,526 elementary children, and employed approximate NHI data to construct three indicators imputed to food insecurity: low birth weight status, economic status (poverty versus non-poverty), and time of year (summer break time versus semester time). We compared ambulatory care for these diseases between children with low birth weight and those not, and between children living in poverty and those not. A difference-in-differences method was adopted to examine the potential for a publicly- funded lunch program to reduce the harmful health effects of food insecurity on poor children. We found that children in poverty were significantly more likely to have ambulatory visits linked with diabetes, inherited disorders of metabolism, iron deficiency anemias, ill-defined symptoms concerning nutrition, metabolism and development, as well as mental disorders. Children with low birth weight also had a significantly higher likelihood of using care for other endocrine disorders and nutritional deficiencies, in addition to the above diseases. The study failed to find any significant effect of the semester school lunch program on alleviating the harmful health effects of food insecurity for poor children, suggesting that a more intensive food program or other program approaches might be required to help poor children overcome food insecurity and its related health outcomes.