This might be too big a question for an ELI5. This is a really old question in psychology, and while there are many competing theories in that time, the question isn’t definitively answered yet.
Our shortest and best understanding is that during the sensitive period of brain development where neurons are still organizing themselves into “discreet” brain parts, babies are getting a lot of really interesting information about what words do. This is an advantage that seems specific to humans (and some birds with learning song), but beyond that there’s a mountain of research trying to figure out how the hell it actually happens the way it does.
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