I usually make certain they are all in bed when I turn the game off for the night (theirs as you can change the daylight setting). If they are tired during the day, you can either "put them to bed" or have them relax in some fashion - watching TV or relaxing on the hammock. They will also 'nap' and "go to bed' on their own when they are exhausted and do it more often if you remember to praise them lavishly if you see them do it while you are watching them. Some activities help them recover energy.