Getting two year old to sleep!!

[tigerfrog]

Anyone out there with a bit of good advice?? Up until 2 months ago my two and a half DD2 had a dummy. Popped it in at bedtime ( 7.30) two minutes later fast asleep and didnt hear a peep until the morning. The dummy fairy took her dummy one night when she moved into a big girls bed and that's when it started!!! I put both DD's to bed at the same time. Read some stories, kiss good night and close the door. DD1 is generally asleep quickly ( although she still sucks her thumb which I cant seem to stop) DD2 lies in bed, clambers around the room, looks at books, dresses herself up, sings to herself everything but goes to sleep. She never cries, she never comes out of the room but I can go in there at 9.30 and she is still awake!! What can i do to encourage her to sleep? Should i worry about it? She doesnt seem to be tired during the day and is always the first up! What is the right amount of sleep for a two year old?