Treat sleep as a learned experience. As much as we'd like to think of sleep as natural, and the ability to do it well as an inborn skill, the fact of the matter is that many healthy sleep habits are learned. Which means that they often need to be encouraged, taught, and reinforced -- often on an ongoing basis.
Establishing habits in children as early as possible is a parenting benchmark and a cornerstone of adult self-care. When children push nighttime boundaries, parents become chronically over-tired. That makes them less likely to maintain the necessary routines in the first place, which sets up a vicious cycle.