The key to giving your peeps enough rest is to let them sleep overnight without checking on them or bothering them. Most 'real' people sleep many consecutive hours a day. When you keep checking on your peeps, they think you want them to be awake so you can play with them. They'll try to get fitful bouts of resting in, but it won't be enough. Just turn the game off (without pausing) and let them get some rest. It should work wonders after a day or so of that.
But Lady, they don't get 8 hours of sleep; they get years of sleep in game time, like virtual sleeping beauties. I really don't want to leave and come back to find them years older. Much can happen in 4 (or 8?) years, kids can leave home, mother can pass child bearing age, they may get sick and perhaps die. I really want to witness how the family evolves, and I really feel that there should be a way for us to be able to do that rather than closing the game and so closing our eyes.
And there's another problem about it. I usually leave the game about 3 AM and come back next day afternoon. So no matter how I set the day/night, they'll still get half of their night's sleep. And it's quite impractical for me to adjust my life according to my virtual family

So, my little people are constantly taking naps (naps seems to replenish more energy) when they're tired. Their energy bar is usually half full, but it's the best solution I could find without leaving them alone all night.