**Core Concept**
Myoclonus in children refers to a type of involuntary muscle contraction that can be caused by various underlying conditions. The most effective treatment for myoclonus involves medications that modulate the activity of neurotransmitters in the brain, specifically GABA (gamma-aminobutyric acid) and glutamate.

**Why the Correct Answer is Right**
Sodium Valproate is a broad-spectrum anticonvulsant medication that is effective in treating myoclonus in children. It works by inhibiting the activity of GABA transaminase, an enzyme responsible for degrading GABA, thereby increasing the concentration of GABA in the brain. This leads to a decrease in excitatory neurotransmission and an overall reduction in seizure activity, including myoclonus. Additionally, Sodium Valproate has a unique mechanism of action that involves the blockade of voltage-gated sodium channels, which further contributes to its efficacy in treating myoclonus.

**Why Each Wrong Option is Incorrect**
**Option A:** Clonazepam is a benzodiazepine with anxiolytic and anticonvulsant properties, but it is not the first-line treatment for myoclonus in children due to its potential for sedation and dependence.
**Option C:** Phenobarbitone is a barbiturate with sedative and anticonvulsant properties, but it is not effective in treating myoclonus and is associated with significant side effects, including cognitive impairment.
**Option D:** Ethosuximide is an anticonvulsant medication primarily used to treat absence seizures, and it is not effective in treating myoclonus.

**Clinical Pearl / High-Yield Fact**
Sodium Valproate is a versatile anticonvulsant medication that is effective in treating a wide range of seizure disorders, including myoclonus, generalized tonic-clonic seizures, and partial seizures. It is also used to treat bipolar disorder and migraine prophylaxis.

**✓ Correct Answer: B. Sodium Valproate**