Tragically, 936 children have died in hot cars since 1998. Wisely, NHTSA has prioritized evaluation of sensor systems in vehicles for the ability to detect unattended children and prevent heat stroke occurrence.Recently, innovators have developed systems that detect children present in the vehicle by measuring carbon dioxide (CO2) in the vehicle cabin, but there is no test method to assess whether or not these CO2 sensor systems are working properly.Thus, the purpose of this project is to develop the CO2ATD - a manikin the exhales CO2 in a manner similar to a 12 month old, or 3 or 6 year old child.The CO2ATD itself, which is a humanoid structure of dimension and mass distribution of a human 12 month old, has an upper airway including nostrils and mouth similar to that of a human. The CO2ATD inhales air from the cabin and exhales CO2-enriched air to the cabin, at a breathing rate, tidal volume and CO2 concentration similar to the 12 month old or 3 or 6 year old child, as specified by the test technician. Breathing is accomplished in a Lung that is connected to the CO2ATD via a Trachea which terminates at the nostrils/mouth.