I have had the EXACT same problem... except that my daughter (just a month or so younger than yours) just transitioned into her big girl (toddler) bed, and while she used to sleep until 8, she started getting up earlier each day, and this morning she got up at 6, and I was like "no way." However, I tried this with her a few months ago and the same thing happened, so I was prepared this time. I think that, once they figure out they can get up on their own, their desire for freedom trumps their need for sleep. Izzy was also napping either not at all (she would get up and play in her room) or much shorter. I basically have had a no tolerance policy towards it- for the time being, at naps and at bedtime, I leave her door open about 5 inches and sit outside her door (I don't plan on doing this long, just until she gets used to the idea that I am watching and she can't get away with it) where she can't see me but I can hear/see enough to know if she is in bed or not. If she gets up I put her back without saying anything to her. And when she gets up too early in the morning I tell her "it's still time for sleeping" and walk her right back to her bed, then I go back to bed. The first few mornings I didn't get much sleep and she kept getting up, but I kept doing it- I also wasn't as strict in the mornings, if she got up and played in her room I didn't go in unless she was being loud. But this morning when she got up at 6 I put her back to bed and we both went back to sleep until 8. It was great! While I don't think an earlier bedtime will help, I do think it is related to lack of sleep because they start getting up earlier, then they would rather play than nap, and it becomes cummulative. That was why I decided to be such a nazi about bed and nap time for the time being, so I know she's getting the sleep she needs and hopefully is getting in the habit of staying in her bed. You may also want to try a later bed time, but it probably won't help much.