Toddler Sleep

Hi there, my DD is almost 2 1/2 years old and went into a big girls bed almost two months ago, however since then she is getting up at 4am, 5am etc the latest she will sleep in 6am.
She has cut out her day sleep pretty much but she still goes to her room for an hour of "rest" time and if she falls asleep its great and if not thats fine too.

When she was in a cot she used to wake around 4 or 5 and i would hear her talk for a minute or so and then she would go back to sleep, i think now she is in a bed she just gets up because she "can".

Im tempted to put her back into a cot but im not sure if she is too old for that or what to do. Any ideas?

I have tried telling her to wait till its light outside etc but nothing seems to work. She comes into our bed when she gets up but doesnt go back to sleep she just talks to herself in there and mucks around.

I think it's a change of season thing too, Z has started waking bright and early at 6am recently from her old standard of 7:30 - quite an adjustment for us!

However, when she wakes before 7, she's told it's still nighttime and she needs to stay in her room. She can 'read' books, play with her toys, or go back to sleep, but she needs to be in the room. Thankfully she can't open the door herself yet.... when she does.... I don't want to think of it

Also, a word on bedtime - I actually find, at this age, that they usually wake around the same time regardless, however, sometimes bringing the bedtime forward actually results in a bit more of a sleep-in, backwards as it sounds. I think it falls along the lines of sleep begets sleep - or certainly that an overtired child sleeps less well than a rested one.