It didn't happen to me and truthfully I don't know how it didn't, DS didn't sleep day or night and I lived on autopilot, it was sheer luck. But then I've locked him in the car in 34 degree heat, we've left DD at pre school for nearly an hour with both of us thinking the other had got her. Non child related but I am so sleep deprived today due to my own health issues that I completely lost my bearings in our car park and nearly drove into a pole - I had no idea what level I was on and swung round to go down again but was already down.
I could never believe this could happen as an accident, but having had two non sleeping children I do believe it is possible. Someone thankfully told me to put my nappy bag on the back seat which I did and still to this day I check the back seat of my car for kids and they are 8 and 5. I don't do it because I'm a better organised parent, I do it because I live my life in sleep deprivation and accidents happen.