Mine have always had a night owl type bodyclock, even as babies, they wouldn't wake in the morning till gone 8.
We get into a bit of a bad routine in the summer holidays, because I am also a night owl, so we all find ourselves waking later and later and going to sleep later and later.
Whilst it's "only a problem if it's a problem", they do need to be up earlier for school and son gets a bit anxious if he can't sleep in the summer, even though I explain to him that it's because he woke later and only needs a certain amount of sleep, so this summer i might draw the line at 8:30am and set an alarm for us all to get up then, even if we then just hang about for a while and not actually get dressed till a little later when we might go out.
On a school day I try to wake them by 7:45 so it's not too much of a rush.
Whilst it is nice as it gives us the option of a lie in on weekends (though mine are getting to an age where they get their own breakfast and entertain themselves), there is definitely something to be said for being an early riser, imagine all the time you'd have before school if you were up and awake at 6am.
Friends hate me when this is discussed, not that I bring it up, but it does come out from time to time and they cant' believe my luck but it goes both ways a bit - like i say the school week would be easier if I didn't have to literally peel them out of bed and shake them into a uniform some days.
Son has recently taken to setting an alarm for 7:15, getting dressed and getting his breakfast on a school day, which then gives him an hour to play on his xBox before school, which works well as he gets off to sleep at a more reasonable time at night.
Daughter could benefit from that but seems to want to sleep. So do I, but I always set my alarm for 7:30 on a school day.
So I'd say, it's only a problem if it's a problem. You might well find that this is their natural body clock and you'll always be working against it to have them up earlier, and therefore you need a proper reason to do so, and school/preschool etc will provide that and it will fall into place then, and no reason to stress about it till then.