i have brought up my kids and other childrens too and over the years have learned the do and dont.
this is my advice but check with your gp.
never encourage too much food after a bug. but increase the fluid cos he could be highly dehydrated. during a bug we lose a lot of body fluid take this seriously.
avoid pure juice ,fizzy stuff, but encourage water with little honey and little sqreezed lemon juice? NO snacking and he is going to taste you for that.
r establish a good family meal around the table . give him a little to eat even if it is 2 spoonfuls.
Ignore the tamper tantrums but reinforce the good manners around your table.if he refuse to eat, fine warn him you are about to take his food away.
be firm , and patient. snacking: i use to peel some chuncky carrots and give it to the childrens or piece of banana.
no crisps and rubbish and do not show anger. good luck and it works.