A child not sleeping as early/late/long/peacefully as his or her parents expect is one of the most common topics of conversation in my consultations – even if that was not the main reason for making the appointment! If the child doesn’t sleep well, neither does the parent and after a while that gets everyone down.
One of my registrars has written a helpful leaflet on this topic which neatly summarises most of what I say in these situations – and what I tried to do (with varying degrees of success) when my own children were younger. It is available here.