Sadly, I think it's a rapid change in at least urbanized predominantly white societies.
This is why recently I've been loving watching old videos of people living their everyday lives before technology oversocialized us.
Here's a recent one that I happened to find because I was researching the Boston accent:
https://www.youtube.com/watch?v=omVFxtbZoyw
These days you'd think all these people were just actors in some 80's movie, but they were real people all walking up to each other and interacting organically. Nobody is staring down at phones, everyone is socially confident, kids are out playing, adults show affection towards the children, and so on. Some may disapprove of the lifestyle of these urban Boston Italians or certain things they say, but it's one reflection of a different time that really wasn't that long ago. This was before mainstream media scared the shit out of people and convinced them that the world is too dangerous, before people overexposed themselves on social media, before video games addicted children, before adults spent more time with their devices than with their families. Things weren't perfect in the old days by any means, but there were some good things about humanity that we've gradually suppressed in ourselves which we've been losing in a short period of time.
Like you, I grew up with a big family where the little ones were sometimes seen naked whether it was when we were running around in the dirt or taking baths together. By a certain age, our parents knew when to start having us to always wear clothes and bathe by ourselves. But there's what I would consider a precious window of innocence in young childhood where kids can exist and be themselves, clothed or not, free of the knowledge of sexuality. My sibling and cousins all were naked at one point or another as young kids and nobody feels scarred or exploited because our elders saw us naked in some vague memory.