1. Buy small breathe mints.
2. Have each child put one in their mouth, everyone at the same time.
3. The winner is the kid who has their mint last the longest.
The trick is they need to keep the mint in one place as much as possible. If they move it around in their mouth in order to talk, it will dissolve quicker. The more quiet and still you are, the longer it will last.
We played it first with Mentos Now Mints and then I had them try Altoids. They refuse to do Altoids ever again. If Altoids stay in one place too long, it really starts to burn. So as fun as it was for me to witness, it was against the point of the game because instead of being still and quiet, there were a lot of shrieks and moans coming from the back seat of the car.
If we ever go on a long road trip, I think the Quiet Mint Game will come in handy!