Depending on the age of the child, the amount of activity and stimulation during the day seems to make a difference in the quality of and amount of sleep achieved at night. With our little ones, if they haven't had a nap or have outgrown their nap and have a "big day" with more activity than normal, then they seem more prone to waking in the night. On days like this, I start the bedtime routine earlier to give them more of a chance to settle down for the night."