Hi! My DD is EXACTLY the same age as yours and we seem to be having a very similar problem! It's 20:30 and she's been in bed since 19:00 and is still awake!! Last night she fell asleep @ 20:15, woke around 5am but resettled until 7.05am this morning. She's only taking an hour nap in the day and that seems to be at random times despite putting her down at the same time. Tonight, as I said, she's still awake....seems fairly settled but during this past hour and a half, she's been babbling away on and off. It's doing my head in as I think i'm doing something wrong too! Perhaps we aren't! Perhaps it's just like you say, something to do with their development??!! So, not sure I can help but wanted to acknowledge a share in this problem with you for support (to each other).