What is the reason for my 5-year-old child to throw up frequently for the past three days?

Hello,

Welcome to icliniq.com.

As per the information provided, your child is underweight and short of stature for the age, which requires proper workup. There is an extensive list of causes when vomiting is concerned, so it will not be good on my part to jump on any diagnosis without a detailed history. It can be some infection, or it can be some other problem with the stomach or intestine, related to the brain, or some changes in body metabolism. Vomiting can occur due to any stress condition. I would like to know more details on how it started? Is it recurrent? Is there any fever, any change in bowel motion, any abdominal pain, or any change in behavior or alertness? Are they passing urine well? Has the child consumed any untoward eatables? Etc.

Meanwhile, you need to keep the child well hydrated with ORS (oral rehydration salts). I would suggest Pedialyte ready to use solution (ORS) approximately 150 mL after each vomiting.