**Core Concept**
Supracondylar fractures of the humerus in children are a type of elbow fracture that occurs just above the condyles (bony prominences) of the humerus. These fractures are common in children aged 5-7 years and are often associated with a fall onto an outstretched hand, resulting in a flexion-type injury.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology and treatment of supracondylar fractures in children. The most common type of supracondylar fracture is the extension-type fracture, which accounts for approximately 97% of cases. This type of fracture typically results from a fall onto an outstretched hand, leading to a hyperextension injury of the elbow. The typical treatment for this type of fracture involves closed reduction and percutaneous pinning or casting.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the typical presentation of a supracondylar fracture in children. While flexion-type injuries can occur, they are much less common than extension-type injuries.

**Option B:** This option is incorrect because it is not a true statement regarding supracondylar fractures in children. The treatment of supracondylar fractures typically involves closed reduction and percutaneous pinning or casting, not open reduction.

**Option C:** This option is incorrect because it does not accurately describe the typical age range for supracondylar fractures in children. While these fractures can occur in children of various ages, they are most common in children aged 5-7 years.

**Option D:** This option is incorrect because it is not a true statement regarding supracondylar fractures in children. The most common type of supracondylar fracture is the extension-type fracture, not the flexion-type fracture.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the treatment of supracondylar fractures in children involves closed reduction and percutaneous pinning or casting, and that the most common type of fracture is the extension-type fracture.

**Correct Answer: D. The most common type of supracondylar fracture in children is the extension-type fracture.**