Infection-related skin manifestations can present in this way, and sometimes they take on a Christmas tree like distribution at the back. This is secondary to a viral infection and is called pityriasis rosea
This is a self limiting condition and antibiotics are not required.
If the lesions are itchy, then antihistamines will help.
You can apply calamine
lotion on the areas.
If the areas do not appear bruised and he has no fever
, then it is not something to worry about.