T.S.
"The American Academy of Pediatrics now recommends that kids resume eating a normal, well-balanced diet appropriate for their age within 24 hours of getting sick"
From: https://www.webmd.com/children/brat-diet
Keep it simple (rice, noodles, broth/soup) and avoid fried, acidic and spicy food.
I would also add that it's perfectly okay for kids to get "tired" of something and still have to deal with it. It's a life lesson, in this case it's learning how to how to respect your body, and take heed of doctor's orders.