It depends on how long you are "out of town". If it's just half the day then make sure that you buy them enough food (if you have enough money, of course).
The easiest thing to prevent starving while absent, just pause the game with the SPACE key. You'll read "GAME PAUSED" in the little display in the middle. Make sure that you do this with EVERY family that you play.
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There are 10 people living on this planet: those who understand binary and those who don't.