Fille has 2 meanings in French - "girl" and "daughter" depending upon context (whereas they have 2 words for "boy" and "son", garçon and fils ).
As the French would use the word fille in both instances when referring to a girl or daughter, here, on DL, I think it is meant as a vocab exercise for us, the learners.
Personally I think the splitting of hairs with "daughter" and "girls" is unnecessary. We can understand the distinction and still realize that in English, both girl and daughter are acceptable to mean daughter. I think insistence on such rigidity in DL translation is unnecessary. The same goes with "belle" and "jolie". After a while it gets tiring.
I agree completely with you Seattle.... we need to remember, that Duo is a free language course and pre programmed into a computer... and I think Duo is the best programmed unpaid course that I know. I have abandoned a paid language course in favour to Duo. sometimes it just takes a little more time of research, if an answer is marked incorrect and you think it is correct.
Have I missed something here? The hints give "sympas" as nice and "droles" as funny or amusing. Why then, when I put their daughters are nice and amusing (which I think is more of a compliment than "funny") am I corrected to "their daughters are kind and amusing"? Am I not allowed to mix and match? I have reported it! At a second attempt, "kind and funny" was accepted, so mix and match is O.K. - except for kind and amusing, Weird!
If someone tells me 'Their girls are delightful/nice/funny/amusing etc', I know it means their daughters. It's completely normal in English to say 'their girls' to mean 'their daughters' (even adult daughters). Interestingly, it is much less common to do this in the singular, except perhaps of people who have only one daughter but also sons.
It seems like in both english and french "girls" and "daughters" can be interchangeable, depending on the context.
If you don't provide any structure to the sentence that makes it clear you're referring to one or the other, then don't mark people wrong because you were too vague to specify.
I don't know why Duo refuses to acknowledge that "leur filles" can be either their daughters or their girls. This is so annoying and problematic since BOTH are CORRECT. We who are learning need to know that BOTH are CORRECT or we are at risk for misunderstanding what French speakers might say to us.
In English, certainly in the UK, the use of nice and x means very x or acceptably x, or comfortingly x as in "This tea is nice and hot". "My boss is nice and distant. He's in Paris, I'm in London. Perfect!"
The way to keep nice in our target sentence is to insert a pause, marked by a comma, after nice: "Their daughters are nice, and funny". Or just choose another adjective: friendly, lovely, delightful, well-mannered.