WHEN a little girl is six and a little boy is six, they like pretty much the same things and enjoy pretty much the same games. She wears an apron, and he a jacket and trousers, but they are both equally fond of running races, spinning tops, flying kites, going down hill on sleds, and making a noise in the open air. But when the little girl gets to be eleven or twelve, and to grow thin and long, so that every two months a tuck has to be let down in her frocks, then a great difference becomes visible. The boy