Probably the first post-apocalyptic novel that I ever read was in 7th grade English--Mrs. Crowley or Crawley, something like that. I detested the teacher--she made us diagram sentences, but we'd never been taught the parts of speech (how I got to the 7th grade without learning the parts of speech is another problem). But one thing was good about that 7th grade English class--the required reading was O.T. Nelson's The Girl Who Owned a City.
The short story: A deadly virus kills everyone on earth over the age of 12, leaving the children behind to fend for themselves. Gangs form, battle lines are drawn, etcetera. One girl named Lisa forms a group of her own, and in order to defend themselves against other gangs, she decides to build a fortress to protect them from everyone else.
The story itself is one of several sub-sub-genres of the Pandemic subgenre: the adults-are-all-dead plague. Typically, stories with this particular plot tend to be Young Adult fiction, just as this book is, because isn't it a great fantasy of all kids that there are no more adults in the world to tell them what to do? And since adults write books, isn't it the job of adult writers to show children how terrible it would be and destroy the collective fantasies of children everywhere?
I LOVED this book as a kid; as an adult I find it dated and a little flat. The dialogue isn't that great and the characterization is, well, about what you would expect from someone who really only wrote one book (and it was written to generate capital to pay his workers at his house painting company, wtf). On top of all of that, Nelson isn't shy about pushing Objectivism onto kids. In fact, that was the whole point he wrote the book--to help explain Ayn Rand's Objectivism to the youngsters. I'm not really sure that was the message I came away with all those years ago. I got more of a "thank-God-my-parents-aren't-dead" vibe.
However, for kids between 10-14, this book would be an awesome beginning to the genre.
I would give it 4 out of 5 stars for nostalgia's sake, but probably only 2.5 out of 5 without it. The short moral to the book? Kids are psychopaths without adults around to control them. Be happy you aren't living in a world where they run the show. Remember Lord of the Flies?