I kind of remember my daughter going through something similar and I think it was a couple of things. First, she wasn't getting enough intellectual stimulation or physical stimulation for her liking/need. Second, it was her chance at exercising her control. "I cry... they come"... my parents also spent a significant amount of time caring for her since I couldn't afford childcare while my husband and I both worked. I do think she is old enough to know what she is doing...but possibly not old enough to stop doing it. The only way would be that approach to sleep where you comfort after so many minutes and wait longer and longer amounts of time in between visiting.... and I was a total failure at putting it into practice because my second- who is six still has sleep issues. Another thought occurred to me as I was typing, I think there was another point where she was just over-tired. Maybe start a log of when this happens to see if you can find any consistencies. Whenever I have done this to track behaviors something has always turned up.