**Core Concept**
The child's presentation, characterized by painful flexural eruption, erythema, peeling, and blistering, is indicative of a severe autoimmune skin disorder. The involvement of flexures and the presence of flaccid blisters suggest a specific protein family defect.

**Why the Correct Answer is Right**
The child's symptoms are consistent with a diagnosis of **Bullous Pemphigoid (BP)** or **Bullous Pemphigoid-like disease**, which is an autoimmune blistering disorder. The disease is characterized by autoantibodies targeting the **Bullous Pemphigoid Antigen 2 (BPAG2)**, also known as **Collagen XVII**. This protein is a member of the **Collagen family** and plays a crucial role in maintaining the integrity of the skin's basement membrane.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Collagen type I** is a major component of skin and bone, but it is not the primary target in Bullous Pemphigoid.
* **Option B:** **Elastin** is a protein that provides elasticity to skin, but it is not directly involved in the pathogenesis of Bullous Pemphigoid.
* **Option D:** **Keratin** is a protein that forms the cytoskeleton of epithelial cells, but it is not the primary target in Bullous Pemphigoid.

**Clinical Pearl / High-Yield Fact**
Bullous Pemphigoid is a classic example of an autoimmune disease that requires early diagnosis and treatment to prevent complications. Immunofluorescence studies are crucial in confirming the diagnosis by demonstrating autoantibodies against the basement membrane zone.

**Correct Answer: C. Collagen family**