I think the disconnect might be in terms of the age that is considered to need special attention. Go back a few hundred years and you were expected to contribute and behave as an adult once you were hitting something like 8-11, as I recall.
And it is also true that even up to the beginning of the 20th century, child development was basically considered as being a linear development from being nothing to being an adult. Children were just stupid adults. It was the likes of Piaget and Vygotsky starting in the 1920s who identified that children have fundamentally different cognitive processes to adults, and that stages of development add new modes rather than replace these processes.
Heaven lies about us in our infancy!
Shades of the prison-house begin to close
Upon the growing Boy,
But he beholds the light, and whence it flows,
He sees it in his joy;
The Youth, who daily farther from the east
Must travel, still is Nature's Priest,
And by the vision splendid
Is on his way attended;
At length the Man perceives it die away,
And fade into the light of common day.
That's published 1807. I was just looking up Du Fu's poems about his son from a thousand years before that, e.g.:
Jizi is a fine boy,
last year was when he learned to speak.
He asked the names of our visitors
and was able to recite his old man’s poems.
I pity his being so young in the turmoil of the times,
the household poor, he looks to his mother’s love.
I didn’t succeed in taking him to Deergate,
8 and I can’t expect something tied to a wild goose’s foot.
I realise these don't address your point directly but I must have come across countless examples from various cultures of people having a far less crude attitude than in your second para; it would be surprising if not really, given the number of loving mothers and fathers who've raised children and will have noticed the kind of things that maybe were only expressed in a scientific idiom later.