The Cameron family was enjoying an afternoon meal when they took their eye off their eldest daughter, Nancy.
As the family left in two separate cars, both Cameron and his wife, Samantha, thought their daughter was with the other. They realized their mistake a few miles down the road.
Samantha Cameron arrived within 15 minutes to pick her up. The girl had been in a restroom when the family left. She was fine when her mother picked her up.
The administration said the incident happened "a couple of months ago."