The Girl Who Owned a City

When a plague sweeps through the world and kills off anyone over 12 years of age, the children of the world are left without anyone to care for them. So when young Lisa decides she's sick of scavenging for food and fearing the new young gangs that roam the area, she decides to unite the survivors and lead them back to the way things were, even though nothing will ever be the same.

Published in 1975, the book is still considered a popular choice for required reading in schools, due to the depth of characters and subject matter. It must be mentioned than many of the political themes have particular appeal for budding Objectivists, something the author was more than happy to provide.

This book contains examples of:

 * Artistic License Biology: No disease that kills that fast, with a 100% fatality rate, could spread that quickly.
 * Broken Aesop - Lisa goes on a great deal about rightful ownership etc., but the fact remains that she is a scavenger.
 * A case could easily be made that she believes ownership ends at death. After all, she's not at all hypocritical about not stealing supplies from the living (although it could be considered dubious that she's the only one owning the school when Jill, Craig, Steve, Charlie and Todd all claimed it along with her at the same time and indeed helped build the "city" as it was). The book would have made a better case if it acknowledged this point about only the living retaining their ownership rights, though... And of course, the fact that the main source of conflict is over a school building, presumably something paid for with tax money, and thus belonged to a public society which, even if dissolved, makes her only argument that she is the rightful the fact that she was there first.
 * A case could also be made for the fact that these are kids and kids are not exactly the world experts on property rights. Quite a few children in the age group of the characters in the book are firm believers in the Finders-Keepers Rule, as well as the Dibs Law and the No Take-Backs Accord. Add in the survival drive brought on by catastrophe and regardless of being made "older than they are" by the hardship, they're still going to hold to an understandably childish view on who gets what for which reasons.
 * Cosy Catastrophe - A world full of dead adults is surprisingly rot and disease free and, for the protagonist, apparently more fun than she's ever had before. It's also remarkably free of children injuring themselves, and the older children tasked with caring for infants and toddlers seem to be a little too responsible for their age.
 * Easily Truth In Fiction. Young children forced into hard times of any sort tend to be "older" than they really are out of simple necessity. When you're constantly worrying about whether or not the people you love will be able to feed themselves regularly, you simply don't have the luxury of being a typical boisterous youngster ignorant of the hardships of life and the need for responsibility to survive.
 * Great Big Book of Everything - Lisa is said to have gotten most of her ideas on what to do from "a great book." Said book is heavily implied to be Atlas Shrugged.
 * She read that at 12 years old?
 * Improbable Weapon User - One of the children, afraid of hurting someone with an actual gun, suggests using fire extinguishers to scare people away.
 * This causes Fridge Logic when you know how fire extinguishers work and having that stuff sprayed at you would likely be much more debilitating and painful than a quick death from a bullet.
 * Only Fatal to Adults - The Plague
 * Sequel Hook - The liner notes said that O.T. Nelson was working on a sequel, but this never came to pass for fans. There was never any stated reason why, but this entry on Answers.com says that the publisher said it didn't stand up to the original - though there are no references on the answer to check.
 * Talking the Monster To Death - Lisa literally scolds an enemy leader into surrender.
 * The Caligula: Lisa, quite possibly. She has shown an aversion to voting and sharing, she at times seems to have a lack of empathy, and thinks everyone should be forced to fend for themselves and that this apocalyptic situation is fun, and individuals like that usually grow into sociopathy.
 * The Complainer Is Always Wrong - Everyone who isn't Lisa. Jill in particular.
 * There Are No Adults - Literally.
 * Undermined By Reality - One of the examples Lisa gives for why it's a good idea for her as an individual to be an "owner" of a city is cities like that worked fine pre-crisis, specifically mentioning the Republic of Minerva... which didn't work out at all.
 * X Meets Y - Atlas Shrugged meets Lord of the Flies.