Police reports were compared to the information provided by a hospital monitoring system for children under 15 years old injured as pedestrians and bicyclists by moving motor vehicles in Orange County, California. The analysis was limited to identifying caveats in the police report database. Underreporting by police was conservatively estimated at 20% for pedestrians and 10% for bicyclists. Comparison of the pedestrian databases suggested underreporting by police of incidents involving 0-4-year-olds, nontraffic incidents, incidents in which the vehicle was backing up, and cases not involving a child crossing a street. Comparison of the bicyclist databases indicated an underreporting by police of nontraffic cases. These caveats, in part, are related to police agency reporting requirements. The police injury severity scale was found to correlate poorly with a scale based on medical diagnoses, and substantial underreporting by police of serious injuries was demonstrated. We suggest that utilization of police injury severity scales be limited to categories of fatal, injured, and not injured (when available).