A New York City man is accused of sexually assaulting a child under 16 while working at a youth camp, Bergen County Prosecutor Mark Musella said. Jelani McKenzie, 32, of Queens was arrested Friday and charged with four counts of first degree aggravated sexual assault, endangering the welfare of a child, and three counts of aggravated criminal sexual contact, authorities said. On July 23, Alpine Police contacted the prosecutor’s Special Victims Unit about the alleged sexual assault of a child that began in March in Alpine. An investigation by the prosecutor’s office and the Alpine Police found …