I totally agree with your idea :-)
I realized a few years ago that having a subject to dive in with my friends is a real promise that it will be a great lunch, I’ll try to introduce that regularly with them :-)
About children, when mine were at school, I was a mother “alone” and I remember that I was very attentive to have real conversations with other adults (friends, neighbors, …) and say to the children same kind of things that you propose. I was thinking about me, 8 years old, for lunches or dinners, waiting and listening, learning what is to agree or disagree, how to argue and dig on subjects, and this new generation wich is so less in contact with that that they have real difficulties to … have conversations !
I love conversations as an art :-)