I didn't click your link yet, because I'm not in the mood for anything sad.
I get what you mean about being scared of forgetting your kids in the car. I used to worry about that a LOT. I can be absent-minded, so I was horrified at the possibility. It's one thing when someone makes a poor judgment and leaves their children in a car while they run errands; but when they didn't even realize their child was in the car, that just makes it so much sadder. The thing is, I always have my kids with me. Always. So getting them is ingrained in my routine. When people forget their kids, it's usually because of a break in routine. They have their children with them at a time when they usually wouldn't, and so they totally forget about the kid even being in there. (Especially if he's rear-facing and asleep.) So that is one advantage I always had, that transporting my children was never a break in routine.
However, we still had "locked in the car" drills. As soon as my daughter was old enough, we practiced unbuckling, climbing into the front, and opening the door. I said if we ever got in a wreck and Mommy didn't wake up, and it gets hot, do this to get out. We also practiced dialing on a cell phone, where to find it in the car, etc. When the younger ones were born, I taught her that if they were ever alone in the car (or if I was unconscious) and she had to get out, to leave the doors open for the other kids. That's all you can do, right?