I've never really seen 남자아이 and 여자아이 used outside of Duolingo lessons. 소년 And 소녀 seem to be more common. I'm aware they don't have quite the same meaning, but what actually is the distinction and why do I never see the former used?
If i hear this sentence in daily life, i would interpret it as "(나는) 남자아이는 기억이 나요" which means "I remember 'the' boy (but not others)"
Of course, either interpretations make sense, but Duo's answer is bit like a sentence from a typical korean learning book.
It seems like people are typing out the answers but it just gives me words to choose from. Ive looked in settings but can find anything about it. Is there a way to change it so i can type out the korean and English answers?