Please do not take your child's anxiety issues lightly. At any age. Not only teenagers are affected by anxiety and loss of self esteem. A very young child needs good positive self confidence reinforcement as well.
It is imperative that you listen carefully to what your child is telling you about how he feels. In what manner does he feel painfully disabled? What specifically is he experiencing? You may have to ask him rather forcefully, but lovingly, what is going on in his life. But, somehow, he must TALK to you. You may even have to do some behind the scenes investigating.
Anxiety is a serious health problem, for adults as well as children. Actually anxiety is quite common. In adults it is easier to find out the symptoms, but for children it is much more complex.
Does your child panic easily? Does he say he does not want to go to school? You must wonder why. Does he complain of an upset stomach, headache, muscle aches and pains? Does he relate sleeping problems, such as waking up in the night, or not being able to go to sleep? Have you noticed a change in his eating habits?