Good idea. This kind of thing happens often enough that people should adopt some trick to jog their memory. or maybe cars could have a sensor, like you left your lights on.
I like that trick too... but with 4 kids I almost always have a kid in the car. however I will say that I have been in the house before noticing my 4 year is not with us. I sort of have gotten use to my older kids letting my younger kid out. twice in two weeks the older kids just closed the car door. can you imagine trying to get out of criminal responsibility by saying your kids usually let your other child out and and you got distracted by a business call or worse... fighting leftist trolls on elitetrader?