"Excuse me, are your children already here?"
Translation:Извините, ваши дети уже здесь?
My answer was marked incorrect: Извините, твои дети уже здесь? However, there was nothing in the English sentence "Excuse me, are your children already here?" to indicate that formal speech needs to be used, or that the question is to multiple people, so I have reported, as I think твои should be accepted as an alternative to ваши.
You used the informal 'твои' with polite "извините"
Извини, твои дети уже здесь?
Извините, ваши дети уже здесь?
Thanks so much for the explanation, I did not know that excuse me had formal and informal variants! Therefore, by that logic, is здравствуйте a polite form of hello and здравствуй an informal alternative?
извини, твои дети уже здесь? is still considered incorrect, I reported. Please make the correction, this has apparently been reported 3 years ago already.
твои has a singular 'you', ваши a plural 'you' (but both of these are inflected for the main noun being plural). 'твой' (and thus of course твои) is used when there's only 'one' of you, and when not particularly concerned with being very polite. If there's more than one of 'you', or there's reason to be polite, ваш (and ваши) are used.
So, ваш functions like "y'all's" but without the connotations of being a country bumpkin.
Since you ask about твой vs. ваши I am a bit unsure about whether you have understood the bit about these pronouns agreeing with the owned thing as well.