Here is a summary from Wikipedia
In 1982's The Disappearance of Childhood, Postman argues that what we define as "childhood" is a modern phenomenon. He defines "childhood" as the period from around age 7, when spoken language is usually mastered, to around age 17, when written language is mastered. Not coincidentally, these ages correspond to the typical school years.
The word "child" originally meant "son or daughter"; only in modern times did it gain its second meaning of "a person between birth and full growth". Prior to modern times, children were considered "little" adults, rather than today's conception of them as "unformed" adults.
In medieval times, children and adults "lived in the same social and intellectual world" (p. 36). Children dressed the same as adults, shared the same labor and pastimes (gambling was considered a normal childhood pursuit), and with literacy confined to special classes (the monks, for example) had similar intellectual levels. Few children attended school. Children were not shielded from the harsh realities and shameful secrets of the adult world. Adults did not conceal their sexual drives, nor was there a high level of "civilized" mores defining certain behavior, body functions and characteristics as distasteful. "Without a well-developed idea of shame, childhood cannot exist" (9). To Postman, the middle age's absence of literacy, education and shame explains their absence of our conception of childhood.
Postman credits the invention of movable type printing to the idea of childhood. With literacy came adult "secrets", information available only to adults who could read. And literacy required schools to teach people how to read. "Because school was designed for the preparation of a literate adult, the young became to be perceived not as miniature adults, but as ... unformed adults": (p. 41). These two factors created a new social hierarchy — adults now had "unprecedented control over the symbolic environment of the young" (p. 45). For Postman, 1850–1950 was the "high-water mark of childhood." Children's birthdays began to be celebrated, and their welfare became viewed as something special that needed protection. Children gained specialized clothing and literature — different from adults. Childhood became viewed as an idyllic time of innocence.
In 1950 came television and the disappearance of the child. Television is an egalitarian dispenser of information. No longer were there adult realities and secrets — these were dispensed in news, commercials, and programs to people of any age. Childhood's innocence was lost and the idea of shame became "diluted and demystified" (p. 85). Television, which became the dominant source of information (over books), requires no specialized learning, further diminishing the distinction between children and adults. Some television content adultifies and eroticizes children; some television infantilizes adults. Television has created a three-stage life cycle: infancy, adult-child, and senility (99).
His evidence for the disappearance of childhood: the rise of crime perpetrated by and against children; the increase in sexual activity and drug/alcohol abuse in children; children and adults sharing musical tastes, language, literature, and movies (many big budget movies are comic books that would have been marketed solely to children years ago); the lack of differentiated clothing styles (little girls in high heels, grown men in sneakers). Even childhood games have been replaced by organized sports (Little League, Pee Wee, etc.) which are more like adult sports. "Adulthood has lost much of its authority and aura, and the idea of deference to one who is older has become ridiculous" (p. 133).
He makes a point that civilized behavior acknowledges our animal urges (sex, violence, etc.), but makes them secrets that are kept hidden from children. Since they are no longer secrets, our society may become more barbarian. A case in point is foul language, which is no longer kept hidden from children, and has become more predominant everywhere.
While positing his theory, Postman offers no solution for society on the whole. Even as he wrote in times before the widespread availability of the Internet, he acknowledged that there is probably no turning back from our visual, electronic age. Thus, he writes, "Resistance entails conceiving of parenting as an act of rebellion against American culture" (p. 152).
from the wikipedia article.
The 2005 Norway conference took place AFTER postman's death in 2003