I have a hard time understanding how someone could "forget" their child is in the car. I have three, 21, 19 & 17. My wife and I managed not to " forget " them in the car, not once, not ever.
Apparently it happens rarely. So it doesn't happen for the large, large majority of us. But that doesn't mean it couldln't happen to someone else, someone who doesn't have evil intent or bad character.