Welcome to health care magic.
From your description, It seems to me that your son may be having either pityrosporum folliculitis
or acneiform eruption. You can Google for images and compare. Pityrosporum folliculitis is an yeast infection and subsides with a course of itraconazole
orally. Acneiform eruption can be drug induced and responds well to topical benzoyl peroxide
. Please avoid steroids
Hope this helped you.
You could send me the pictures if you want further clarification. I will be glad to help.