Incorrect answer to Spanish question
The question was "La niña camina" ... mark all correct answers. I marked only "The girl walks" - duolingo marked this as wrong saying there was an additional correct answer "The child walks". If the question was "El niño camina" then I would expect both to be correct. I checked with my Mexican wife and she agrees - a non-descript child would be referred to as niño and NEVER niña.
"La niña camina" the solution is "The girl walks". I agree with you, the word child is usually used in Spanish as a masculine form: "El niño camina". But don't worry, you know the difference between "niño" and "niña", and that's the important thing.
I think that if you mean to say 'the child' you say 'el niño' - but if you know this is a female child you say 'la niña' even though in English you would say 'the child'.