Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern.
Numbness or parathesia of tongue can be due to many reasons
1. Trauma-Any injury to the tongue may cause pain as well as damages receptors or nerves of the tongue may lead to numbness. Common injuries may be a result of eating or drinking very hot foods and beverages, strong acids or alkalis, tongue piercings or biting the tongue
2. Infections- A number of infections may involve the tongue causing numbness. The most notable of these is a
herpes simplex virus (oral herpes) or reactivation of
varicella zoster (
chickenpox virus).
3.Dental Surgery-In some cases there may be
nerve damage during the course of the dental procedure causing numbness
4. Due to toxins & poisonous agents
5. Rarely it may be result of brain related problem
First of all take your son to a oral physician/
dentist for checkup, he would evaluate if there is actual loss of sensation or its just psychological & treat accordingly
Hope this information helps