What is this all about

This week is one of the weeks that Claire goes to summer camp and when I took her on Monday she totally freaked out on me. She went to this same school all last year twice a week and never once cried or said that she wanted to come home with me. However, both today and on Monday she cried and clung to me as I tried to leave. Cory took the day off of work on Monday so we thought maybe she was sad because daddy was home and she thought that she was missing out on something, but when we picked her up she was all smiles. When we asked her why she was crying like that when we left, was it because daddy was home, she said no, she didn't want mommy to leave. She and I talked about it yesterday and how she didn't need to cry because I would be back to pick her up after lunch, she said okay and that she wouldn't cry today. Even in the car on the way there she said "I not cry today okay mommy"? I told her that sounded great, HOWEVER, as soon as we started walking down the hall and approached the room she started clinging to me like a dryer sheet to a pant leg. We got into the room and she saw all of her friends, but it started all over again the tears and calling for me. I even told her that I would read her one book and then I was going to leave and she couldn't cry, she agreed I read the book and then when I went to leave, oh boy. The teacher came over and picked her up to distract her as Paige and I made a run for it. I don't know what this is all about, but I am really nervous because she is starting a different preschool in the fall and if she is acting up like this at a school that she is familiar with for a year now, what is it going to be like at a new school with new surroundings and new friends?