**Core Concept**
The treatment of tuberculosis (TB) in children requires the use of effective antitubercular medications to prevent the spread of the disease and promote recovery. **Isoniazid (INH)** and **Rifampicin (RMP)** are the cornerstone of first-line antitubercular therapy, as they exhibit potent bactericidal activity against Mycobacterium tuberculosis.

**Why the Correct Answer is Right**
Rifampicin is a potent inducer of the enzyme cytochrome P450, which is responsible for the inactivation of isoniazid. The combination of INH and RMP is synergistic, allowing for a reduced dosage and duration of treatment. **Isoniazid** inhibits the synthesis of mycolic acid, a critical component of the mycobacterial cell wall. **Rifampicin** inhibits DNA-dependent RNA polymerase, preventing the transcription of essential genes.

**Why Each Wrong Option is Incorrect**
**Option A:** **Ethambutol** is an important second-line antitubercular agent, particularly in cases of resistance or intolerance to first-line drugs. It is not typically used as a first-line treatment in children.
**Option B:** **Pyrazinamide** is a first-line antitubercular agent, but it is not typically used as a monotherapy in children due to the risk of resistance. It is often used in combination with INH and RMP.
**Option C:** **Streptomycin** is an aminoglycoside antibiotic that is used as a second-line antitubercular agent, particularly in cases of resistance or intolerance to first-line drugs.

**Clinical Pearl / High-Yield Fact**
In children, the treatment of TB often requires a combination of antitubercular medications, including INH, RMP, and pyrazinamide, for a duration of at least 6 months.

**Correct Answer:** A. Isoniazid (INH) and Rifampicin (RMP)