Final answer:
In most states, it is illegal to leave children unattended in a vehicle at any age. The exception to this rule is when children are supervised by someone who is at least a certain age, usually 12 or 13 years old.
Step-by-step explanation:
In most states, it is illegal to leave children unattended in a vehicle at any age. This is because it can be extremely dangerous for children to be left alone in a vehicle, as they can be at risk of heatstroke, abduction, or injury. The exception to this rule is when children are supervised by someone who is at least a certain age, usually 12 or 13 years old.
Example: In California, it is illegal to leave a child 6 years old or younger unattended in a vehicle without the supervision of someone who is at least 12 years old.