Welcome to HCM & thanks for writing in.
Henoch schonlein purpura
occurs in childhood.It is usually accompanied by fever ,joint pain,abdominal pain
.Does your grandson has any of this?
HSP is usually self limiting ,paracetamol tablets for pain and fever are all that is required.
A renal function test is to be done.
Usually it subsides on its own but sometimes it may become chronic.
A visit to dermatologist
will confirm the diagnosis .
Hope this helps.
I wish him good health.