You have got to consider that movies like this were produced in the era of outdoor movie theaters where less than 50% of the audience actually watched the movie at all. The windows of the car were likely so steamed over that they couldn’t see the movie if they occasionally glanced at it.
I can't say for my older brother and I but I'm pretty sure that my younger siblings are the result of tripple features.
Without getting out of the driver's seat, my Father would stash us onto the roof of his station wagon with a sleeping bag and we couldn't get down until he retrieved us.