My DS (19 months old) has had various stages of waking up at an unreasonable hour - 5.30am or so. I've tried all sorts of different methods - earlier bedtime, later bedtime, wake to sleep, etc without much success.
However, I recently read a report about trying to alter their circadian rhythym by taking them outside for a walk/play/etc later on in the evening. He usually goes to bed at 7pm so I have been taking him out for a walk/play about 6-6.30pm just before bath/bed. And it has had a fantastic effect - he is now waking routinely between about 6.15 and 7.00am which I find much more reasonable.
So I just wanted to let any mothers of early risers know in case they wanted to give it a try!