Hi, it may be a viral infection. There are various causes of mouth lesions like Herpes
, Crohn's disease, Behcet's syndrome, Sjogren's syndrome, Hand foot and mouth disease etc. Please consult an oral pathologist or oral surgeon. It is very difficult to comment on the pathology without actual examination. Please ask you son to use chlohex mouthwash and Betadine
gargles alternatively. You need to give him painkillers for temporary relief. Application of mucopain ointment 3-4 times a day on the ulcers may also be helpful. Take care!