It is illegal to leave a child age six or younger unattended in a vehicle on a hot day:

It is never a good idea to leave a child unattended in a car. It is illegal to leave a child age six or younger unattended in a vehicle. A child may be left under the supervision of a person age 12 or older.

• Even if they are secured in a child passenger restraint system.
• If they are supervised by a person twelve years of age or older.
• Only if the key is in the ignition.