In classical writing there were 5 topics (or here) that helped you develop your theme. All of these topics can easily be turned into questions to develop a conversation. They are definition, comparison, circumstance, relations and authority. There are whole books (and curricula) written on how to use these approaches but here is a quick primer.
Andrew Kern, of the Circe Institute, says that the best question to ask is "Should X (a character) have done Y (an action)?" Should the ants have shared food with the grasshopper? Should Calpurnia Tate tell her mother that she wants to go to college? This simple question opens the door to great conversations about motivation, outcome, cause and effect and more. There is even a process to help your child learn how to do this by themselves as they think about story and history. Simple but effective.
The other offering I have for you is a more organized approach that teaches you how to use Socratic questioning in the framework of the narrative arc. Whaty what what?? Socratic questioning is a technique used to help students find the gaps in their knowledge so that they realize what they don't know and can begin to search for answers to those questions. It is learning through thoughtful questions instead of telling children what to think. The narrative arc (scroll through - it's on the 3rd page) is the general outline that every good story goes through.
The Center for Lit has developed an 8 hour DVD seminar about teaching classic books. I haven't seen the seminar - I just got the workbook and have enough background to figure out how it works. There are 173 questions that can be used to help explore character, setting, scene and more from picture books to War and Peace. This book can be used for all your children throughout their lifetime. It can help you get more out of what you read as well.
BONUS - Did you know that Mortimer Adler, who tried to pull together all the great works in the Great Books of the Western World through Encyclopedia Britannica, created a list of 103 themes that are found throughout literature? There are lots of creative ways these subjects could be used, followed and discussed in the literature and history your child is reading. I heard of one teacher (who had students for multiple years) who had the kids pick a few themes or ideas that intrigued them and asked them to follow it through the books assigned for that year. As a parent you could do a similar thing with your middle schooler and up. Consider encouraging your kids to have a journal of themes in what they are reading (and you can lead by example).
Another day we can talk more about what to read.