I leave my kids in the car with one of my older teens. I guess I would say if a child is old enough to legally babysit, then they should be old enough to be left in a locked car.
This is Arkansas law on leaving a child in a car unattended:
Leaving Children or Pets Unattended
While the state doesn't have any specific laws concerning leaving children or animals unattended in vehicles, common sense dictates using extreme caution when doing so, especially during periods of excessive heat or cold. If you see an endangered child or animal, call 911 and give the vehicle location.