In Japan, all citizens are covered by the national insurance system. Children's medical expenses are subsidized by local government co-payments. This removed most economic barriers to visiting medical facilities, geographical obstacles to pediatric medical services remain, including distance to medical facilities and transportation time. However, information on geographic accessibility of pediatric inpatient services is scarce. In this study, I calculated the proportion of children resident in areas accessible to pediatric inpatient service providers within 30 and 60 minutes by automobile. Calculations were based on addresses of hospitals that met criteria for high reimbursement for secondary and tertiary pediatric inpatient services, data for residential blocks, and data for the average velocity of an automobile. In total, 88.0% of children lived within 30 minutes of these hospitals and 95.2% of children lived within 60 minutes. The percentage of children with such access was higher in regions with high population density (e.g., Kanto and Kinki) compared with regions with low population density (e.g., Hokkaido, Tohoku, and Shikoku). Furthermore, regions with high population density also had high rates of children that lived within reach of hospitals with at least five full-time pediatricians.