Sum up what someone said before you answer, until they say "yes, that's it".
Listening without interrupting, letting others finish and respecting different tastes are habits children use far beyond the dinner table.
Kalmdix announces the mission as a playful quest at the start of the meal, then lets the children talk about whatever they like. It works on one habit over five meals; on the fifth, the mission is a secret. Kalmdix never says who did or didn't do it: the results appear after the meal.