**Core Concept**
Pneumothorax in a child with pneumonia suggests the involvement of a specific bacterial pathogen that causes necrotizing pneumonia, leading to the rupture of lung tissue and air leakage into the pleural space.

**Why the Correct Answer is Right**
Staphylococcus aureus is a common cause of necrotizing pneumonia, particularly in children. The bacterial toxins and enzymes produced by S. aureus cause lung tissue damage, leading to the formation of cavities and pneumothorax. The presence of S. aureus is often associated with a severe and aggressive course of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Streptococcus pneumoniae is a common cause of community-acquired pneumonia, but it is less likely to cause necrotizing pneumonia and pneumothorax.
**Option B:** Haemophilus influenzae can cause pneumonia, but it is not typically associated with the development of pneumothorax.
**Option C:** Klebsiella pneumoniae can cause severe pneumonia, but it is more commonly seen in adults and immunocompromised patients.

**Clinical Pearl / High-Yield Fact**
Staphylococcus aureus pneumonia often requires aggressive treatment, including antibiotics and supportive care, and may require surgical intervention in severe cases.

**Correct Answer: C. Staphylococcus aureus**