Final answer:
The child's symptoms after spinal fusion surgery indicate a possible serious complication, and the nurse should immediately notify the healthcare provider for further assessment and prompt management.
Step-by-step explanation:
When a child complains of abdominal discomfort and begins to have episodes of vomiting along with noted abdominal distension after spinal fusion surgery, these can be signs of a potential serious complication such as an ileus, infection, or bowel obstruction. The nurse's action in this scenario should be to notify the healthcare provider immediately (C). Prompt assessment and diagnosis are crucial to manage any potential complications postoperatively. It is not appropriate to administer antiemetics, encourage ambulation, or continue routine care without further instructions from a healthcare provider.