your son could be suffering from infection of the skin of the penile area. if he is having problems with urinating or feeling pain when urinating you will require a urine test done to rule out an infection.
you can give him a course of antibiotics and apply an antiseptic cream after cleaning the affected area with antiseptic solution and give him brufen
syrup or tablets to reduce the redness
personal hygiene is also important.
hope to have answered your query