GENEVA — The level of violence against children and cases of cholera in northern Mali are rising at an alarming rate since the area was seized by al-Qaida-linked Islamist fighters and Tuareg rebels following a March coup, U.N. officials said Friday.At least 175 boys between the ages of 12 and 18 have been recruited into armed groups, at least eight girls were sexually assaulted and two teenage boys were killed by land mines and unexploded ordnance since the end of March, the U.N.