I wrote " parents' " but the correction showed that I had written " parents ".
Yes, same here. And told me I was almost correct. The same happens with these English apostrofes in plural when learning other languages as well.
If you write parent's, however, the answer is rightly rejected, but parents (with no apostrophe) is accepted as correct.
I still can't see any pattern in how Duolingo treats punctuation marks; a little earlier I had an answer in the German course rejected for leaving out a question mark (which has never happened before to me). I wish it were consistent.
is still incorrectly marking "parents'" as a typo....that apostrophe is needed