**Core Concept**
Volvulus is a condition where a portion of the intestine twists around its mesenteric attachment, leading to obstruction and potentially compromising blood flow. In children, the small intestine is the most common site for volvulus, but other areas can also be involved.

**Why the Correct Answer is Right**
The least common site of volvulus in children is the stomach. This is because the stomach is a relatively fixed organ that is less prone to twisting compared to the small intestine. However, volvulus of the stomach can still occur, particularly in cases where there is a pre-existing condition such as a gastric duplication cyst or a congenital anomaly. The stomach's fixation to the diaphragm and the presence of the gastroesophageal junction also make it less susceptible to volvulus.

**Why Each Wrong Option is Incorrect**
**Option A:** The small intestine is the most common site for volvulus in children, making it an incorrect answer.
**Option B:** The large intestine (colon) is a possible site for volvulus, but it is not the least common site in children.
**Option C:** The sigmoid colon is a relatively common site for volvulus in adults, but it is not the least common site in children.

**Clinical Pearl / High-Yield Fact**
In children, volvulus is often associated with a congenital anomaly or a pre-existing condition. A high index of suspicion is necessary to diagnose volvulus, as the symptoms can be non-specific and may mimic other conditions such as appendicitis or gastroenteritis.

**Correct Answer:** D.