"Ці діти ваші?"
Переклад:Are these children yours?
You can say "These children are yours?" but the word order changes the meaning slightly. Usually the question word (in this sentence are is the question word) should come first. As you have moved it from the normal position, it reads more like a statement that you think is true but need to check. The word order in this way is also used to express surprise, like "Wow! These children are yours?!"
If there isn't this extra meaning to the sentence, we would usually say "are these your children?" or "are these children yours?"