Final answer:
Children typically lose sensitivity to non-native language sounds by about 1 year old, as they become more attuned to the phonemes used in their environment's language.
Step-by-step explanation:
Children lose sensitivity to sounds that are not part of the language spoken around them by the time they are about 1 year old. During the first year, infants can differentiate between the sounds of all human languages, but this ability narrows down as they get closer to their first birthday, leaving them able to discriminate only among those phonemes that are used in the language or languages in their environments. This developmental milestone is important for language acquisition and is a sign that babies are tuning into the specific sounds necessary for understanding and speaking their native language.