Your son seems to have acute urticaria
There is itchy erythematous rash
on various parts of the body.
There may be some cause.
It may be infection somewhere in body,allergen,irritants,infestation ..etc.
You consult dermatologist
for perfect diagnosis.
He might advise some investigations.
and then treatment may be given.
Antihistaminics may given.
Treatment of the cause is must.
If there is severity, steroids
may be given in tappering dose.
I hope you got my answer.
Dr. Ilyas patel MD