**Core Concept**
Children typically develop language skills in stages, with most acquiring a vocabulary of 4-6 words around 15 months of age, while their primary mode of communication and social interaction remains non-verbal. This phase is characterized by the use of gestures, pointing, and facial expressions to convey meaning.

**Why the Correct Answer is Right**
At 15 months, children often use a limited number of words to communicate, but they also rely heavily on non-verbal cues like body language and facial expressions. This stage is a critical period for language development, as children begin to associate sounds and words with meanings. The limited vocabulary and reliance on non-verbal communication are hallmarks of this developmental phase. Children at this age may use words in isolation, but not yet in combination to form simple sentences.

**Why Each Wrong Option is Incorrect**
**Option A:** 12 months is too early for children to have a vocabulary of 4-6 words, as most are still in the babbling stage and have not yet begun to use words to communicate.
**Option C:** 18 months is too late, as children typically have a more extensive vocabulary and are starting to use words in combination by this age.
**Option D:** 24 months is significantly beyond the age range for this developmental phase, as children at this age are typically using a more complex vocabulary and engaging in more verbal communication.

**Clinical Pearl / High-Yield Fact**
Remember that language development is a gradual process, and children may exhibit a range of skills at different ages. However, a vocabulary of 4-6 words and reliance on non-verbal communication are key indicators of language development at 15 months of age.

**✓ Correct Answer: B. 15 months**