Eve,
My son is 6 and still only just manages to sleep throught the night 4 out of 7 times. Otherwise his regular wakeup time is somewhere between 4 and 5.30am daily, which as you can imagine has awful consequences for how he is expected to last through a full day of education in year 2!!
We have had cranial osteopathy which has so far had results, but not directly with his sleeping, but just generally with his behaviour, emotions and ability to get through the day with his younger brother and sister - who by the way, sleep fantastically!
We are about to engage in another bout of treatment ( I say "we", my husband is a non-believer!), and I will let you know if it finally pays dividends and gets us past the dreaded 5am!