Why is my sons willie hurting he is only 4 HELP?

MY LITTLE BOYS IS 4 YEARS OLD AND HE HAS TH CHICKEN POCS. BUT FOR THE LAST 2 WEEKS HE HAS BEEN SAYING HIS WILLIE IS HURTING AND WHEN HE GETS PICKED UP HE SAYA MY WILLIE MY WILLIE CAN ANYONE HELP PLEASE THANKS DAWN