Suggest Treatment For Rashes On Kids Leg

MY NINE YEAR OLD SON SPRAINED HIS KNEE FOUR DAYS AGO. XRAYS WERE TAKEN AND BLOOD WORK WAS DONE TO CHECK FOR INFECTION. RESULTS WERE FINE. THIS MORNING HE HAS DEVELOPED A RASH ON HIS LEG FROM THE KNEE DOWN ONLY THAT KINDA LOOKS SIMULAIR TO POISON IVY. COULD INFECTION HAVE SET IN, OR WOULD THIS BE CONSIDERED NORMAL?