We, too, enjoyed/enjoy our family dinner conversations. The topics covered a wide range of ideas. Interesting news, catching each other up on our activities while we were apart, philosophical and existential questions, international and science developments, extended family plans. We also made it a group decision and effort to decide what to give for gifts for birthdays and holidays, and that was always a fun topic.
We also used this time to get to know each other better so we'd pose questions about what their likes, dislikes, favorites, etc. When they were young, we'd ask questions that helped their understanding about their school subjects (history, etc.) If they could invent a new animal, what would it be? What they would do if they were president/king? What do they think is the best form of government and why? As they grew...choose a social world problem to solve and how would they solve it (hunger, poverty, global warming, water shortage, AIDS, cancer, human trafficking, etc.).
Remember that those parlor talks spurred many a revolution throughout history. Start them early to develop the thinking and reasoning process. And most important: teach them to question everything.