Look up the "conditioned head turn procedure" as a means of testing phonetic perception in infants. It is pretty well established that infants have a much greater ability to distinguish phonemes compared to adults.

What you said is true the other way around too. Infants can't look something up in a dictionary, or ask a bilingual person to clarify the finer points of a word or phrase in a language they already know. Infants aren't just learning the language but also the concepts behind the language, which would seem to make what they're doing more exceptional than adult language learning.