Upside Down

There is a phase through which all my children have passed some time between 1 and 5, lasting for years, during which being turned upside down will fix almost anything that is wrong with them. It gives them a joy that seems to wipe away all sorrows. I did it for Zhen Zhen this weekend, when she was distraught over some squabble over toys. And then I got to thinking about it, so I picked her up again and had Mary take this picture. Ben joined of his own initiative. What is it, do you suppose, that makes being upended such a pleasure for little ones?