**Core Concept**
The first sound produced by a child is typically a bilabial sound, which is made by the closure and release of both lips. This sound is a fundamental aspect of phonetics and is often considered a milestone in a child's language development.

**Why the Correct Answer is Right**
The bilabial sound is produced when the upper and lower lips come together to form a complete seal, creating an obstruction in the oral cavity. As the air passes through this obstruction, it produces a distinct sound. This sound is often referred to as a "b" sound, as in "boy" or "ball." The bilabial sound is a key component of many languages and is typically the first sound a child produces around 6-9 months of age. The production of this sound involves the coordination of the lips, jaw, and tongue, which is a complex task for infants.

**Why Each Wrong Option is Incorrect**
**Option A:** A sibilant sound is a hissing sound made by placing the tongue behind the upper teeth, which is not typically the first sound produced by a child.
**Option C:** A fricative sound is a type of consonantal sound produced by directing air through a narrow channel between two articulatory organs, but it is not the first sound produced by a child.
**Option D:** A monolabial sound is not a recognized term in phonetics, and the correct term is bilabial, referring to the use of both lips.

**Clinical Pearl / High-Yield Fact**
The production of the bilabial sound is often used as a milestone in assessing language development in children. Parents and healthcare providers can use this sound as an indicator of normal language development, and any delays in producing this sound can be a red flag for potential language disorders.

**✓ Correct Answer: B. Bilabial. The first sound produced by a child is typically a bilabial sound, made by the closure and release of both lips.**