You just gotta love a mother who tries to cook her baby son twice in one day in a car, accidentally of course. Frail perhaps? Maybe she was stressed? Methinks she needs to chill a bit and then focus. While it is less of a problem nowadays with remote car locking, let me stand on a big box and tell you something.
Never ever put your keys down inside your car. Keys go into an ignition switch. Otherwise, they should either be in your hand or on your person. They don't go onto a seat because your hands are full. They don't temporarily sit in the boot while you pick things up. Just do not put your keys in the car unless it is into the ignition switch.
For the purposes of this post, children = pets. Don't be cooking either of them.