I have watched a few Doco's over the years and have heard a few times that sleeping patterns are supposed to be genetic... In my case I have to disagree.
My Mum said that she could never get me to sleep untill about 9pm, unlike my 3 older sisters who would sleep much earlier (they thought it was totally unfair that the baby of the family went to bed later than them). I used to wake up at about 8-9am.
My DD has always been an early riser, she is 4 now and wakes up before the sun at about 4.30-6 am in the morning, her bedtime is 7.30pm.
My friends two kids go to bed at 7.30-8.30pm and wake up at 9-10am, she has always slept in as well.