Because they are refering to both girls and boys or boys in general when they end with the o cansados if they use cansadas they will be refering to a group of girls and since ustedes was in there it means that there are refering to both girls and boys ustedes means you all
But I believe Ustedes could be referring to a group of all women as well. I think consadas should be accepted.
I have had many sentences in duolingo recently where ustedes was translated as all of you. My answer should be accepted.
"Y'all" is a regionalism and so should be recognized as a word that some people use. I, myself, prefer to use "all of you" when translating "ustedes," even though the pronoun "you" is both singular and plural, as well as being a subject pronoun and an object pronoun. I use "all of you" in translation because it is less objectionable to native Spanish speakers, who have a hard time remembering that the English pronoun "you" does not need clarification.
In normal speech, the inflection rises at the end of both Spanish and English sentences.
Why was "Are they tired today" counted wrong? When I saw "están", I knew the sentence context was "plural" so I hovered over the hints and saw "you all" and "they". I do not like to use "y'all" or even "you all" so I entered "they"... I reported that my answer should be an accepted translation...