Amnesty International is accusing U.N. peacekeepers of indiscriminately killing a 16-year-old boy and his father and raping a 12-year-old girl in separate incidents in Central African Republic, the latest in a series of sexual and other allegations against peacekeepers there. U.N. Secretary-General Ban Ki-moon is “personally dismayed and disappointed,” his spokesman said Tuesday. “We would like to emphasize once more that no misconduct of this nature will be tolerated,” Stephane Dujarric told reporters. The U.N., however, has no powers of criminal investigation or prosecution, leaving it up to peacekeepers’ home countries—which U.N. officials often don’t name publicly. …