"Are these your children?"
Translation:Это ваши дети?
Это functions as a pronoun here, meaning "these are", and not as an adjective. The question can be rewritten as "these are your children?" You could say "эти дети ваши?" which would translate to "are these children yours?" because эти is an adjective that describes "children".
Why is это дети ваши not accepted? This way ваши is emphasized, because that is the focus of the question. And in a previous question, это вода ваша was translated as "Is this water yours?": https://forum.duolingo.com/comment/11610940
(Note: Yes, I've noticed that the order in English is different, which adds more emphasis to "yours", but the focus is on "yours" in both cases, because the water and children are existing information.)
That translates a slightly different sentence: "Are these children yours?" and I think they want to teach the distinction between the two uses of это: as a demonstrative adjective, and as a demonstrative pronoun (i.e. attached to a noun, or not). See https://forum.duolingo.com/comment/11536858.
I agree, in almost any situation the English sentences, and also the Russian I think, would amount to the same thing. I suspect some of these distinctions are stressed here because they're stressed in Russian schools - but there's probably a reason for that...
It can be hard to know when a free translation is allowed, or even required. I don't think they had the resources to go over the course with a fine-tooth comb, making everything consistent.
Agreed. It is a different story when you learning from a teacher in person. Here we have a computer program, but still, I am thankful that I am progressing, building the vocabulary and be able by now to have a simple conversation or even watch a movie. It is a journey. There was a day when I did not know a single word. Bit by bit I'll get there....