**Core Concept**
Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by Mycobacterium leprae that primarily affects the skin, nerves, and mucous membranes. Intermediate leprosy is a form of leprosy characterized by a mix of skin lesions, nerve involvement, and a relatively preserved immune response.

**Why the Correct Answer is Right**
The child's symptoms of a hypo-pigmented anesthetic patch on the face are consistent with intermediate leprosy. Leprosy can cause nerve damage, leading to loss of sensation (anesthesia) in affected areas, which is a hallmark of the disease. In the early stages of leprosy, lesions may appear as hypopigmented patches, and the loss of sensation can make the skin insensitive to touch, temperature, or pain. The combination of these two symptoms, hypopigmentation, and anesthesia, makes intermediate leprosy the most likely diagnosis in this case.

**Why Each Wrong Option is Incorrect**
**Option B:** Pityriasis alba is a common skin condition characterized by hypo-pigmented patches, but it does not typically cause anesthesia or affect the nerves. Pityriasis alba is more common in children and is often seen as a benign condition.
**Option C:** Nevus anemicus is a congenital skin condition that presents as a pale patch due to localized vasoconstriction, but it is not associated with anesthesia or nerve involvement. It usually appears at birth or in early childhood.
**Option D:** Nevus achromicus, also known as nevus depigmentosus, is a congenital skin condition characterized by a patch of hypopigmentation, but it does not typically cause anesthesia or affect the nerves.

**Clinical Pearl / High-Yield Fact**
In cases of suspected leprosy, a thorough neurological examination is crucial to assess for nerve involvement, which can include numbness, tingling, or weakness in the affected areas.

**✓ Correct Answer: A. Intermediate leprosy**