**Core Concept**
The most common intra-abdominal solid organ tumor in children is a type of neoplasm that arises from the embryonic remnants of the gastrointestinal tract. This tumor type is characterized by its rapid growth and potential for malignancy.

**Why the Correct Answer is Right**
The correct answer is a neuroblastoma, which is a malignant tumor that arises from the neural crest cells in the adrenal glands. Neuroblastomas are the most common extra-cranial solid tumors in children, accounting for approximately 7% of all childhood cancers. These tumors often secrete catecholamines, leading to symptoms such as hypertension, tachycardia, and flushing.

**Why Each Wrong Option is Incorrect**
**Option A:** Wilms tumor, also known as nephroblastoma, is the most common renal tumor in children, but it is not the most common intra-abdominal solid organ tumor.
**Option B:** Hepatoblastoma is a rare malignant tumor of the liver that occurs in children, but it is less common than neuroblastoma.
**Option C:** Rhabdomyosarcoma is a type of soft tissue sarcoma that can occur in the abdomen, but it is not the most common intra-abdominal solid organ tumor.

**Clinical Pearl / High-Yield Fact**
Neuroblastomas can be associated with a range of systemic symptoms due to catecholamine secretion, including hypertension, tachycardia, and flushing. The diagnosis of neuroblastoma often requires a combination of imaging studies, such as CT or MRI scans, and laboratory tests, including tumor markers.

**Correct Answer:** C. Neuroblastoma.