Final answer:
The child's symptoms of stomachache and nausea after eating ice cream are most likely classified as a food intolerance, specifically lactose intolerance.
Step-by-step explanation:
The 4-year-old child's symptoms of stomachache and nausea after eating ice cream are most likely classified as a food intolerance. Food intolerance happens when the digestive system is unable to break down a certain type of food, leading to symptoms such as stomach cramping and diarrhea. In this case, the child may be experiencing lactose intolerance, which is the inability to digest lactose, a sugar found in milk products.