Hi Megan and welcome to the course and community. Yes, it really does matter. Un, Le, Son Ton( A, The, His/Her, Your in order) are all articles which precede a masculine noun and if you get them wrong you will be marked down. Une, La, Sa, Ta all precede a feminine noun. There seems to be no rhyme nor reason as to why a noun is either masculine or feminine, they just must be memorised. Look; a sea La Mer is feminine but a lake is masculine, Le Lac. The Table is feminine La Table but the Window is Masuline Le Fenetre. Believe it or not a vagina is Masculine? Le Vagin! Crazy. You will need to memorise the gender of all. There are some guides but because there are the nefarious Exceptions, they cannot utterly be relied upon. I hope that I've not put you off because it does come with usage and practise and it is so very exhilarating when one remembers a few correctly! It is like "Flying!" JJ.
Odd correction, Que. Maybe Duo has recently broadened its linguistic horizons. I say this because I would have thought 1 enfant would rather be a translation of One Child whilst it is asking to solve A Child which for my tiny brain translates to Un Enfant. I suppose Duo's translation could work but surely only secondarily . Hopefully one of the moderators will explain in detail Duo's take on this.
This is a Duo programming error.
Duo was expecting you to write "Un enfant". If you just wrote "enfant" then it will have been registered as a mistake and Duo will attempt to offer you a correction.
Unfortunately in the learning numbers section (un, deux, trois etc) many learners complained about having to spell out the numbers and wanted the numerals to be accepted in translations. Duo gave in and allowed numerals. So Duo was programmed to accept 1, 2, 3 etc as alternatives to "one, two, three" and "un, deux, trois".
Now Duo 'thinks' that "un" and "1" are equivalent and so offers "1" when it should have offered "un".