The reason kids pick up languages and concepts early in life is a result of evolution. It has nothing to do with self-awareness and disregard with social norms. It's the complete opposite. Survival of early humans depended on learning and communication. When we were hunter/gatherers cooperation and socialization meant survival. The faster you learned language and social skills (i.e. hunting or gathering) meant an increased chance of survival. The faster you learned, the more likely you were to survive. Language and socialization were key to early human survival and the more you excelled at it, the more you thrived. If you didn't, your more likely to be a victim of natural selection. Humans have an intrinsic nature to conform to what they perceive as "social norms". It's a genetic response.

I don't see how the two (excelling at language acquisition due to lowered social inhibition vs evolving to excel at language acquisition early in life) are mutually exclusive.

This doesn't contradict the previous post. Evolution may have resulted in a mix of adaptive neural physiology and the lack of self-awareness. But perhaps the latter is tempered as a result of the acquisition of language.