Final answer:
The age under which it is illegal to leave a child in a vehicle can depend on the specific jurisdiction, but it highlights the caregiver's duty to ensure child safety and avoid neglect or endangerment.
Step-by-step explanation:
The legal age under which it is illegal to leave a child in a parked vehicle with the motor running can vary by jurisdiction, and specific laws should be checked in your local area. Generally speaking, there is a significant responsibility on any caregiver to ensure the safety and well-being of a child in their care. Examples of the duty of care concept include not leaving young children unattended around potential dangers such as bodies of water, poisons, flammable materials, or in this case, vehicles with the engine running. The given scenario evidences the moral and legal imperative that is placed on a caregiver not to expose children to situations where there is foreseeable risk of harm.