To be specific, Postman in The Disappearance of Childhood (1982) makes the claim that childhood is a social artifact of modern times, which I suppose means that the concept of a "childhood" and the way we perceive it today did not exist in the past. How true is this, how is this idea viewed in academia and have other scholars proposed/wrote about/agreed with this? and what works can one recommend for understanding history of childhood and social history of children?
There is always more that can be said, but /u/mikedash posted an answer some time ago that discusses this (in the context of Philippe Ariès's Centuries of Childhood, which is the origin of the claim).