Although Silas's scenario was (purposely) pretty far over the top, let me be the Devil's Silas's advocate for a moment here.

About the grandma VT mentioned, who is said to have left the children in the car and gone to do an errand, only to have a stroke and the kids died, presumably (given the ongoing subject of this thread) from heat in the car. If you're worrying about possible tragic results from what "might" happen, she equally might have taken the children (didn't say how many, but let's say two) along, had a stroke in the middle of a busy street and the kids run to her, calling "Grandma! Grandma!" and get run over and killed by traffic, or some other highly unlikely scenario.

Yes, an adult driver should take steps to protect his/her powerless passengers, but if you're hanging it on all kinds of unlikely but possible mishaps like having a stroke, you will NEVER arrive at a foolproof 100% safe line of behavior. Even if grandma stays at home with the kids, with the doors all locked against a possible burglar, there might be a fire, or a satellite may fall on her house, so the kids might be better (or just as badly) off with grandma out in the car.

Dave Oesterreich