**Core Concept**
Digoxin is a cardiac glycoside used to treat heart failure and atrial fibrillation. The dosing of digoxin in children is weight-based, taking into account their body surface area and renal function.

**Why the Correct Answer is Right**
The recommended dose of digoxin in children is 5-10 mcg/kg, which is lower than the adult dose due to their smaller body size and higher metabolic rate. This dose is often administered in two to three divided doses to maintain steady-state levels and minimize toxicity. The dose is also adjusted based on the child's renal function, as digoxin is primarily excreted by the kidneys.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the dose of digoxin in children is not directly proportional to their weight. A fixed dose of 50 mcg would be too high for smaller children and too low for larger children.
**Option B:** This option is incorrect because the dose of digoxin in children is not adjusted based on their age. Children of different ages may require different doses due to variations in body size and renal function.
**Option C:** This option is incorrect because the dose of digoxin in children is not typically administered as a single dose. Divided doses are used to maintain steady-state levels and minimize toxicity.

**Clinical Pearl / High-Yield Fact**
To remember the dose of digoxin in children, use the mnemonic "5-10 mcg/kg, not 50!" This highlights the importance of weight-based dosing and the need to avoid fixed doses.

**Correct Answer: C. 5-10 mcg/kg**