Don't give them the tablets until they've just about had enough and are ready to go.

Get there right as the game starts. They'll be occupied by all of the TVs for a few minutes while you order and wait for food. Eat and then see how long they last. When they're ready to go, get a few of the tablets for them. That should occupy them for another 30 minutes or so.

Then bribe them with ice cream or something for dessert. That should get you another 20-30 min from the time you order it until they finish it.

Good luck. Hopefully the game is 42-10 by the time you need to leave.