A 2-year-old boy knew enough words to get his grandmother, his sister, his mother and himself to safety when fire swept their mobile home in the Northern California community of Clearlake. Barbara Grady was reading in the living room when her grandson, Sean McBride, emerged from the bedroom with singed hair. "Grandma," he said, "hot, hot. . . ." Grady then saw that the bedroom was aflame. Investigators said the fire appeared to have begun in electrical wiring.