A few years ago, a literature teacher I had was lecturing a boy in my class who was acting pretty childish and defended himself with some excuses about being still a child, so my teacher started saying that in the middle ages he would have been seen as a man, and that little children were seen as retarded adults. I've been wondering about the accuracy of this, but all I get when I try to google this are some clickbait articles about people who didn't shower. Can anyone tell me more about this, or link me something about this? By the way, I apologise for any mistakes, I'm still learning English.
This mostly comes from an important book in the history of the family, Centuries of Childhood from the year 1960 by Philipe Aries. Aries argued, like your teacher said, that, in the middle ages, people didn't appreciate children specifically as children-- they didn't talk about the cute babyish things they did, or make them special clothes that are totally different from adult clothes, etc. They did care for their children, but mostly in wanting them to grow up. According to to Aries, medieval people were happiest with their children when they figured out how to do functional adult things.
This is partly true, and supported by some kinds of artistic and literary evidence. However, since the 1960s, much of Aries' thesis has been disproven and most historians now believe that medieval people loved their children and appreciated that children were different from adults, even if they weren't as interested in chronicling details about their children as modern people are.