Thank you for your query.
As you have not described the exact location of the pain it is difficult to hazard a guess. You can give your son calpol
four hourly to reduce pain. It shall be better to get a thorough examination of the mouth done to know the exact cause of the pain which can be either in the teeth, gums, tongue or even the pharynx. Applying ice pack at the pain site will also provide some relief.
I hope I have answered your query to your satisfaction.
Wishing your son an early relief.