My Grandson Is 3 Years Old. Four Days Ago He

My grandson is 3 years old. Four days ago he broke out into a rash on allparts of his body. His mother took him to the hospital and they thought it was hives but since then they were told it might be a virus.They have treated him with a cream but today he is complaining of pains in his legs so they are worried it could be something more serious. Please advisethem of what to do next.