A very famous improv comedy game is ‘Yes and…’. The first person gives a statement and the second adds something with ‘Yes and..’ Then it’s the turn to the first person and so on. It will be clear by seeing this fragment with kids who plan a party.
To be honest, I don’t know if I can really use it in the restaurant. Maybe when there’s a lot of time and with very open kids. I might try it by starting myself saying ‘Yes and..’ when a child tells a story and maybe the kid will pick it up.