I've got a 7 year old daughter I have to fight to bed every night.  Once she's there, she's fine, she just doesn't see the need to go to bed.  My three year old is a different story.  She stays in her bed maybe 5 to 6 hours a night, then I wake up in the morning and she's in our bed next to me.  She is a sneaky little thing.  I guess it doesn't help having a rat terrier in the bed that moves around at night that I'm used too, and then she comes in.  I guess my body just thinks it's the dog.