**Core Concept**
Hypernatremic dehydration occurs when there is an imbalance in the body's sodium and water levels, leading to an elevated sodium concentration in the blood. This condition can cause neurological symptoms due to the shrinkage of brain cells. **Hypernatremia** is a serious condition that requires prompt treatment to prevent complications.

**Why the Correct Answer is Right**
The most devastating consequence of hypernatremia in children is brain shrinkage, which can lead to **cerebral hemorrhage** or **seizures**. When the sodium level in the blood becomes too high, water is drawn out of the brain cells, causing them to shrink. This shrinkage can lead to rupture of the blood vessels in the brain, resulting in bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because while seizures can occur due to hypernatremia, they are not the most devastating consequence.
**Option B:** is incorrect because it is not directly related to the most severe outcome of hypernatremia.
**Option C:** is incorrect because, although it may be a symptom, it is not the most severe consequence.
**Option D:** is not provided, but the correct answer is related to the neurological consequences of hypernatremia.

**Clinical Pearl / High-Yield Fact**
It is essential to correct hypernatremia slowly to prevent **cerebral edema**, which can occur if the sodium level is lowered too quickly. The goal is to lower the sodium level by no more than 1-2 mmol/L per hour.

**Correct Answer:** D. Cerebral hemorrhage.