A 3-year-old boy at PALS (I'll call him Caleb) locked his baby sister, and the car keys, in the family car, earlier this week.  His mother (I'll call her Ruthann) had strapped her baby in the car seat, then returned to the house to grab the diaper bag and a box of teacher's gifts, letting Caleb run back and forth between the car and the house, while she carted her supplies to the car.

Only to find that Caleb had happily depressed the lock button on the car door and closing the door, before following her back to the house.