<qa>  What is the most common condition in children?Background: Pediatric patients constitute a significant proportion of all ambulance transports by emergency medical services EMS with the most common conditions being trauma, respiratory distress, and seizures. Cardiopulmonary arrest is a less common condition but has a mortality rate in children in excess of 98. Very little evidence is available regarding the effectiveness of prehospital interventions for children. Canadian communities require guidance as to whether their local EMS services should implement full advanced life support ALS measures for pediatric patients. This proposal builds upon the Adult OPALS Study, the largest controlled out-of-hospital study ever conducted worldwide, which is evaluating the impact of ALS programs in multiple Ontario cities on 35,000 adult patients. 