This is a fascinating (and very quick read) e-book that briefly outlines the stories of popes who resigned or were deposed (most of them in much more tumultuous circumstances than Pope Benedict XVI. It's a nice way to get a quick glimpse at how complex our church history is (which offers some great perspective for the struggles of our own days) as well as a nice overview of what the papacy means to us and where it comes from. Also included are a brief historical and biblical overview of the origins of the papacy and a lovely series of quotes from popes throughout the centuries on the concept of the papacy itself.
Although it is clearly aimed at adults, my high schoolers and I enjoyed reading and discussing this together. (There are definitely some uncomfortable stories about the behaviors of bad popes in the past that you may not be comfortable getting into with younger children.)