A former longtime youth skateboarding coach has been convicted of sexually assaulting six children, Philadelphia authorities said. Rodney Watkins, 55, was able to access his victims through Powerfulnailya, a skateboarding club he founded and ran, District Attorney Larry Krasner said in a Thursday news release. On Wednesday, Watkins pleaded no contest to charges involving six victims. Pennsylvania authorities have withdrawn a seventh case against him because the alleged assault had occurred outside of the statute of limitations. The former coach is now convicted of three counts of involuntary d…