**Core Concept**
Primary tuberculosis (TB) in childhood often presents with a different radiological profile compared to adults. In pediatric patients, the primary site of infection is usually the lung, but the disease manifestation can be atypical, making diagnosis challenging. The correct answer highlights the importance of lymphadenopathy in the diagnosis of primary TB in children.

**Why the Correct Answer is Right**
Lymphadenopathy is a common radiological finding in primary TB in childhood. The primary infection site in the lung may not always be visible on a chest X-ray, but the involvement of regional lymph nodes is a reliable indicator of the disease. In primary TB, the lymph nodes, especially the hilar and mediastinal nodes, become enlarged due to the spread of the infection. This is because the TB bacilli are ingested by macrophages in the lymph nodes, leading to their enlargement. The lymphadenopathy is often bilateral and can be accompanied by other radiological findings such as pulmonary infiltrates or pleural effusion.

**Why Each Wrong Option is Incorrect**
**Option A:** Ghon's focus is a characteristic radiological feature of primary TB in adults, not children. It refers to a small area of pulmonary consolidation at the site of primary infection, which may or may not be visible on a chest X-ray.

**Option B:** A normal chest X-ray is unlikely in a child with primary TB. While some cases may present with a normal initial chest X-ray, the disease often progresses to involve the lymph nodes and other parts of the lung, leading to detectable radiological abnormalities.

**Option D:** Pleural effusion is a complication of TB, but it is not a hallmark of primary TB in childhood. Pleural effusion may occur in more advanced stages of the disease, especially when the infection has spread to the pleura.

**Clinical Pearl / High-Yield Fact**
In children with suspected primary TB, it is essential to look for lymphadenopathy in addition to other radiological findings. A high index of suspicion and a thorough clinical evaluation, including imaging studies and laboratory tests, are crucial for making an accurate diagnosis.

**✓ Correct Answer: C. Lymphadenopathy**