I can understand your concerns.
Don`t worry. This episode must be a Gastroenteritis
, a viral one.
Follow the treatment advice for Kawasaki Disease
Get him seen by your Pediatrician
now too for the Gastroenteritis. He might prescribe you medicines like Domperidone
for vomiting and Probiotic sachet/ ORS if needed.
Give him plenty of fluids like porridge/ vegetable soups/ plain water/ curd at home.
Hope my answer helps you.
Wish a speedy recovery for your kid.