Yeah, it might be a virus that is causing the gastroenteritis
The green stool
is because of bile secreted by small intestine
, that comes out rapidly in cases of diarrhea. You need not worry about that.
For vomiting, you may give him syrup Ondensetron 2mg per dose, thrice a day for 2 days.
If he develops fever, you may give him Acetaminophen
syrup in a dose of 15mg/ kg/ dose repeated every 6 hrs.
If the frequency of his loose stools is more, be sure he drinks and eats well so that he does not get dehydrated.
Give him plenty of fluids like water, ORS, vegetable soups, rice based food, banana, porridge and plenty of curd.
But if he develops a high grade fever/ does not drink well/ passes urine lesser than 4 to 5 times in a day/ you see blood in his stools/ he develops abdominal pain/ he is tired- then you must see your Pediatrician
at the earliest.
Hope you find my answer heplful.
Wish a speedy recovery for your son.