Police say four teenagers have been arrested on hate crime charges for throwing rocks at a school bus full of Jewish toddlers. Police say the three girls and one boy yelled epithets last month as they broke windows on the bus in the Brooklyn neighborhood of Crown Heights. The children were not hurt. The case is part of a string of incidents that have stirred tensions between black and Jewish residents in Crown Heights. The teens are all 14-years-old and are black. The flash points have included an assault on a black college student and an attack on an Orthodox Jewish teen. A race riot erupted in 1991 after a Jewish driver hit and killed a 7-year-old black boy. A 29-year-old Hasidic scholar was stabbed to death in the chaos.