Well, it is, but there are some differences between 소년/소녀 and 남자아이/여자아이. Unfortunately I don't know the differences.
여자아이 accepted "female child" as a correct answer, but 남자아이 did not accept "male child". Girl and boy are definitely more accurate, so if "female/male child" isn't accepted as correct, that's fine, I'd just clean this up so they both accept the same type of answer.
is this natural? casually used in everyday language? it feels awkward to gender-specify a kid in Korean, as in when you want to refer to a boy over there, you would likely refer to him as just 'that kid' (그 아이), no?
It's normal to use in conversation. Korean can be very gender specific, so a lot of the time instead of just referring to "that child/kid/person" you'll say "that boy/girl/lady/uncle/etc."
Using gender in Korean also sometimes helps the context, like if you were trying to mention a kid on a playground in front of you and you say "that kid" you'd have to go through more to figure out which one, while "that (male) kid" could narrow it down some
I was answering just from listening to the voice and heard it as "Namja-ey" and i thought it meant 남자의. You can never trust the voice over. Shouldve read it instead...
I think Duolingo wants us to put the one with the capital letter because it is a 'sentence' but I am not 100% sure.
In case anyone was curious, "boii" is sadly not accepted as an answer. I tried, though.