Welcome to HCM.
Your son needs consultation with an ENT surgeon. If the adenoids
are not obstructing the air passage of the tube leading from back of throa to the middle ear (Eustachian Tube) anf if it is not infected, then it can be left alone. It will gradually decrease in size.
If it is infected or causing obstruction, then surgical removal has to be considered.
Wishing you son all the best.