You shouldn't have any problems with excessive tiredness, as long as you do a few simple things.
First, make sure that you're actually playing the game during the family's daytime. Since it doesn't actually get dark in the iPhone version, due to technical considerations, it can be difficult to determine when it's day and when it's night. If you're changing the clock on your iPod touch, which we don't recommend, then you must keep track of what time it is on the device. The time on the device determines the time in the game, and if it's night-time on your iPod, your family will be tired. If you like to play the game during the night, you might try reversing day and night on the game's Options dialog to see if that works better for you.
Second, you don't actually need to put the family members to bed. All you need to do is make sure that you quit the game in the late evening (press the Home button to quit the game) and leave it off until morning. I never put the little peeps in bed, since they will get rest on their own when the game is off overnight. I turn the game off sometime around 10 pm and leave it off all night.
Finally, make sure that you're not working them too hard. Many of the behaviors that you can praise them for will make them tired (such as working all the time), and they will need frequent naps to recover their energy.
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Barbara
Unicorn
Last Day of Work