Hi, Welcome to health care magic, Loss of appetite and vomiting could be due to acute gastroenteritis,viral gastroenteritis or stomach upset but it needs to be evaluated further by clinical examination and necessary investigations. Your son might have to undergo routine blood count,electrolytes,liver function tests with clinical examination of abdomen. You should see a doctor who will know all the above tests and can prescribe below treatment meanwhile detecting diagnosis. He will require antibiotics (quinolones or cephalosporins or antiprotozoals etc.) with antiemetic, antispasmodics and antiinflammatories with prebiotics and probiotics. There might be need of fluid and electrolyte balance in body. Regards,