## Core Concept
The recommended dosage of Vitamin A for children is crucial for preventing Vitamin A deficiency, which can lead to night blindness, weakened immune systems, and other health issues. Vitamin A is essential for maintaining vision, immune function, and skin health. The World Health Organization (WHO) provides guidelines for Vitamin A supplementation, particularly in regions where deficiency is prevalent.

## Why the Correct Answer is Right
The correct dosage of Vitamin A for children between 1-3 years, as per WHO recommendations, is 200,000 IU (International Units). This dosage is aimed at preventing Vitamin A deficiency and its consequences. The interval for such dosages can vary but is often recommended every 6 months in areas where Vitamin A deficiency is a public health problem.

## Why Each Wrong Option is Incorrect
- **Option A:** 100,000 IU - This dosage is actually recommended for children under 1 year, not for those between 1-3 years.
- **Option B:** 400,000 IU - This is higher than the recommended dose for preventive purposes in children aged 1-3 years and could potentially lead to toxicity.
- **Option D:** 600,000 IU - Similar to Option B, this is excessively high for a routine preventive dose and could increase the risk of adverse effects.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Vitamin A toxicity can occur with excessive intake, leading to symptoms like headache, dizziness, nausea, and in severe cases, increased intracranial pressure. Therefore, dosages must be carefully considered based on age and health status.

## Correct Answer Line
**Correct Answer: C. 200,000 IU.**