There's some debate as to when the modern concept of childhood started: it's definitely recent. Through most of history (and, it's assumed, pre-history), children were expected to start contributing to the functions of the household as soon as they were physically able to: in other words, as soon as they could walk and understand instructions. The exception, of course, was the children of the wealthy classes, as soon as wealthy classes came into existence.
Moreover, this wasn't regarded as a bad thing; if you've read, for example, the Little House books, they're full of the intense pride that children had at being contributing members -- acquiring skills and being given responsibilities.
I think the current historical theory is that childhood was just beginning to be regarded as a separate phase, something to be recognised and regarded with sentiment, in the 19th century. (Peter Pan is a good illustration of this.) The extension of effective childhood into the teens is even more recent -- as you say, the 50s and 60s in the US, at least partly because of the baby boom and the backlash against the pressure of WWII, which sent a hell of a lot of teenagers into battle. With that over, the new prosperity basically meant that everyone (well, everyone who was white and middle-class in the US) could have an extended childhood, comparatively free from responsibilities and expectations, of the sort formerly only available to the very wealthy.
Now it's been extended even farther: I swear the wealthy never grow up at all, and an appalling percentage of people in their twenties try not to do so, either! It puzzles me: I loved reaching adulthood. OTOH, I was raised in a family where I started being given simple chores by the time I was 7, and I was praised when I showed maturity and was rewarded with extra freedoms and respect each time I demonstrated my capacity to handle responsibility. Since I really liked being praised and rewarded, it worked very well for me!
yay, another digression
Moreover, this wasn't regarded as a bad thing; if you've read, for example, the Little House books, they're full of the intense pride that children had at being contributing members -- acquiring skills and being given responsibilities.
I think the current historical theory is that childhood was just beginning to be regarded as a separate phase, something to be recognised and regarded with sentiment, in the 19th century. (Peter Pan is a good illustration of this.) The extension of effective childhood into the teens is even more recent -- as you say, the 50s and 60s in the US, at least partly because of the baby boom and the backlash against the pressure of WWII, which sent a hell of a lot of teenagers into battle. With that over, the new prosperity basically meant that everyone (well, everyone who was white and middle-class in the US) could have an extended childhood, comparatively free from responsibilities and expectations, of the sort formerly only available to the very wealthy.
Now it's been extended even farther: I swear the wealthy never grow up at all, and an appalling percentage of people in their twenties try not to do so, either! It puzzles me: I loved reaching adulthood. OTOH, I was raised in a family where I started being given simple chores by the time I was 7, and I was praised when I showed maturity and was rewarded with extra freedoms and respect each time I demonstrated my capacity to handle responsibility. Since I really liked being praised and rewarded, it worked very well for me!