I reckon it is just another little 'stage" they all go through......annoying & tiring though it is........Olivia, when she got to about 2, did a similar thing.......wide awake and up with the larks at 6am.........but only for a few weeks, then it went back to 7am.

It is often in connection with another change (ie a change in day sleep patterns, or a change of season........)

Charlie normally sleeps till at least 7.30am, but started waking a lot earlier when we moved his room around.......but after a week or two, went back to being a late riser.

And Lexie started doing a 5.30am wake for around 10 days, but has reverted back to a 7am wake, thank goodness........

I reckon just go with the flow, with fingers firmly crossed that it is just a 'stage'........