A boy can play a fireman or a cop - although fewer are pretending to be cops, thank God. And although by high school he'll get channeled into safer, duller ambitions, the truth is, he can be anything he wants, realize any of those fantasies. But little girls? Give them dolls, tea sets and toy stoves. If they show a hankering for more bodacious playthings, call them tomboy, humor them for a few years and then slip them the bad news...