Hello and hope you are doing well.
White patches are common in many throat infections. In response to the infection the body produces soft white debris which collects in the tiny indentations in the tonsils called crypts. Repeated salt water gargles will help. Mix one teaspoon of salt in 1 cup of warm water and ask your son to gargle. If the patches increase in size or become painful then consult your doctor.
Hope this helped and do keep us posted.