**Core Concept**
The patient is presenting with signs of a mass effect in the abdominal region, including a palpable mass, colicky pain, and masked liver dullness, indicating a possible abdominal tumor or cyst. The presence of shock-like symptoms suggests a high-risk situation that requires immediate intervention.

**Why the Correct Answer is Right**
The patient's presentation is highly suggestive of a **Wilms tumor**, a type of renal tumor that is common in children. The tumor has likely caused a **mass effect** on the surrounding structures, leading to the observed symptoms. The masked liver dullness is due to the tumor's location in the right lumbar region, which is displacing the liver. Management of Wilms tumor typically involves **surgical resection** and **chemotherapy** to prevent recurrence.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not address the underlying cause of the patient's symptoms. A nasogastric tube may provide temporary relief from vomiting, but it does not address the underlying mass effect.
* **Option B:** This option is incorrect as it does not take into account the high-risk nature of the patient's condition. A focused assessment with sonography for trauma (FAST) may be useful in other abdominal emergencies, but it is not the primary management step for a suspected Wilms tumor.
* **Option C:** This option is incorrect as it does not provide a comprehensive approach to managing the patient's symptoms. While IV fluids may be useful in managing shock, they do not address the underlying cause of the patient's condition.

**Clinical Pearl / High-Yield Fact**
In pediatric patients, a palpable abdominal mass, especially in the lumbar region, should always raise suspicion for a Wilms tumor. Early recognition and management are crucial to prevent complications and improve outcomes.

**Correct Answer: C. IV fluids and surgical resection with chemotherapy.**