After Teaching as a Subversive Activity, I just finished The Disappearance of Childhood, another book by Neil Postman that deals with education, at least broadly speaking. The book was published in 1985, and makes a fairly simple argument:
1. At its essence, childhood is defined by the existence of secrets that adults hide from children, and which children get to gradually discover. By secrets, Postman refers to many aspects of adult life, including money, social relations, sickness, death, violence, etc.
2. Until the invention of the radio, and especially television, it was possible to hide secrets from children. Books cost money, their distribution can be controlled, they can be put on top shelf at home, and they require effort to read. Besides, there are certain things that can only really be experienced by watching them - rather than by reading about them. 
3. Since modern media makes secrets obsolete, childhood has largely disappeared. Or, as Postman put it himself "It means - to use a metaphor of my own - that in having access to the previously hidden fruit of adult information, they are expelled from the garden of childhood."
Overall, I think this is an interesting argument, and many people will probably find themselves agreeing with Postman on this. But to me, the book feels a bit too much like it was a nail to someone with a hammer. I don't think it's an accident that Postman's most lasting work, Amusing Ourselves to Death, was also published in 1985. Postman got a lot right in that book about the impact of media on modern society —but extending this to defining childhood feels like a stretch. My own intuition is that at least in my own case, my childhood was defined more by freedom of having both lots of time and little expectations placed on me, rather than by being naive about the world.
Aside from the core argument, the book unfortunately feels quite similar to Teaching as a Subversive Activity. It's full of diversions and side points which do little to advance the core argument, and seem to be there mostly to show off the author's encyclopedic knowledge. 
 The Disappearance of Childhood was published in 1985, before the internet, and before the iPhone. Given how exponentially harder these inventions have made it to keep secrets from children, even compared to television, Postman would presumably say that by now, childhood essentially doesn't exist.
 Having said all that, I did enjoy a few of the many side points and quips, for example:
"The importance of fairy tales lies in their capacity to reveal the existence of evil in a form that permits children to integrate it without trauma."
"[The disappearance of childhood] can be seen to occur not only in clothing but in eating habits as well. Junk food, once suited only to the undiscriminating palates and iron stomachs of the young, is now common fare for adults. This can be inferred from the commercials for McDonald's and Burger King, which make no age distinctions in their appeals. It can also be directly observed by simply attending to the distribution of children and adults who patronize such places. It would appear that adults consume at least as much junk food as do children. This is no trivial point: it seems that many have forgotten when adults were supposed to have higher standards than children in their conception of what is and is not edible."