**Core Concept**
The question is testing the knowledge of the toxic dose of fluoride in children, which is a critical aspect of pediatric toxicology. Fluoride toxicity can occur due to ingestion of excessive amounts of fluoride-containing substances, such as toothpaste or industrial chemicals.

**Why the Correct Answer is Right**
The correct answer is based on the concept of the "minimal lethal dose" of fluoride in children. The minimal lethal dose of fluoride in children is approximately 5 mg/kg, which can cause severe symptoms and potentially lead to death. This is because fluoride can cause a range of systemic effects, including cardiac arrest, respiratory depression, and seizures, due to its inhibitory effect on the enzyme enolase in the glycolytic pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable as this option is missing.
**Option B:** Not correct, as the minimal lethal dose of fluoride in children is not 2 mg/kg, which is a much lower dose and would not be lethal.
**Option C:** Not correct, as the minimal lethal dose of fluoride in children is not 10 mg/kg, which is a higher dose than the actual lethal dose.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the toxic dose of fluoride can vary depending on the age and weight of the child, making it crucial to consider these factors when assessing fluoride toxicity. Additionally, the minimal lethal dose of fluoride in children is often cited as 5 mg/kg, but it's essential to remember that even lower doses can cause significant harm.

**Correct Answer:** D. 5 mg/kg