that seems to accompany catching Mom and Dad
acting like they might be in love is a fairly recent phenomenon. It dates from the nineteenth century and was originally confined to the upper classes, who could afford separate bedroom
s. Actually, for most humans watching Mom and Dad is not only normal, it's sex education
It is worthwhile to remember that most people don't live in the large apartments and single family homes that characterize Europe and North America. In much of the world, multiple generations are crammed into one household. For America's pioneer forefathers and mothers, and much of the poorer parts of the world, one room is it. Personal space is the size of your bunk.
Which means that if Mom and Dad are feeling passionate toward each other, and it isn't really warm outside, well guess what, the kids are getting a show. I'm sure some shyness comes when the kids get past infancy and have something of a clue, but really if you live under those conditions you have two choices: Get Over It or Keep your Legs Clenched all the time. Of course extended clenching never eases frustration. Frustration encourages 'getting over it'.
But consider what harm is done. Kids learn that sex is normal, which they probably observed in the barnyard. Sex isn't dirty, rather something you do with the person you love and are married to. Not such a bad example, really. And if you don't happen to have Kinsey handy to explain what a clitoris is, Little Johnny can pick up that point by watching what touching down there does to Mommy. Useful info for his own wedding night.
I know it's hard for us modern folks to become accustomed to the idea that our parents are people who actually feel erotic love for each other. After all, in our society children are to be completely sheltered from sex until they're about to be married. That standard is unrealistic, and contributes greatly obssessive sexual attitudes. But our ancestors knew better. They knew and accepted that sex was a normal part of life. And invented the bundling board to make certain kids didn't go too far, while 'sparking'. Much of what shocks us today was old hat decades earlier.
One source: Jay Furnace: The Americans: A Social History of the American People: copywrite 1967, University of Virginia Press.