“WHAT!! Three of ’em, AGAIN??” was how seven-year-old Jimmie Walker reacted following the birth of a second set of live, healthy triplets to his mother. The history-making birth happened just a few minutes after noon on Feb. 6, 1948 at Syracuse’s General Hospital, when Margaret Walker, 40, of Whittier Ave., delivered two girls and a boy less than five years after giving birth to two boys and a girl.