Thanks for your query.Based on the facts that you have posted it appears that your son has pimples
on his scrotal skin.
Most likely these are either Boil ( Staphylococcal infection
of the hair follicle) or sebaceous cysts.
Final diagnosis can be confirmed only on clinical examination .
please consult qualified surgeon or Urologist
for clinical assessment. He will advise you to give him some antibiotics.\