Final answer:
The age at which it becomes illegal to leave a child alone in a parked car with the engine running is set by local laws, often ranging from 6 to 12 years old. This age varies by jurisdiction, requiring consultation of vehicle codes or child welfare laws specific to the area.
Step-by-step explanation:
The specific age at which it is illegal to leave children alone in a parked car with the engine running varies by jurisdiction, as laws regarding child safety are set by state or local governments. In many places, leaving children below a certain age (often ranging from 6 to 12 years old) unsupervised in a vehicle could be considered child endangerment or neglect. To find the exact age for a given location, one would have to consult the local vehicle codes or child welfare laws. These regulations are typically designed to protect children from a variety of risks, including abduction, injury, or death due to overheating or the vehicle accidentally being set in motion.