Long-term consumption of frozen buns may have adverse effects on health

My child is 3 years old and has been feeling nausea every morning for the past half year, regardless of what they eat, they will vomit. The vomiting usually occurs within a few minutes after eating and is jet-like . Although she says she feels better after vomiting, she still cannot eat. However, her eating habits during lunch and dinner are normal, and no such symptoms have occurred. We are at a loss as to how to deal with the problem of breakfast. I want to know the causes of nausea and vomiting caused by children’s breakfast and how to handle it.