When is it OK for boys to be girls, and girls to be boys? Many kids want to look and act like the other sex. For some, it's a phase; for others, it's not. Parents and schools are adjusting. Ilene Lelchuk, Chronicle Staff Writer Sunday, August 27, 2006 Park Day School is throwing out gender boundaries. Teachers at the private Oakland elementary school have stopped asking the children to line up according to sex when walking to and from class. They now let boys play girls and girls play boys in skits. And there's a unisex bathroom. Admissions director Flo...