The "Septembers" have never ever EVER been apart from each other since the 16 summers they've lived. Only Carmen and Bridget were actually excited for the adventure that was about to unfold.
Tibby finds a pair of jeans in Carmen's closet and tries them on. The other girls do so too. Magically, the pants fit each and everyone of them. It was decided the pants were going to be the girl's "journal" for that summer and the summers ahead.