Welcome to HealthcareMagic forum.
Your child is most probably suffering from a gastrointestinal infection
causing fever , nausea vomiting , refusal to food and dehydration
First and foremost maintain good hydration with plenty of water and fluids like ORS or milk or soups or juices.
Give small frequent meals .
For fever you can give an antipyretic like acetaminophen
as per doctors prescription.
If still symptoms persist you should get the child evaluated by a pediatrician
and a course of antibiotics may be prescribed if needed.
Wishing your child good health.