when i was a kid, i was not allowed by my parents to join an adult conversation. its either they leave me to go somewhere where they could talk out of earshot or they would ask me to go out of the room.
now that i am a parent, i dont allow my kids from joining in adult chitchat. why? because you as a parent should furnish an explanation about the conversation and honestly, kids are not that smart to absorb all these knowledge. so why make things hard for you and your kids when you can always talk discreetly with your adult friends.