What's wrong with 'Those are your children"? Isn't it true that is one child is male and one female, when referring to both you would use he masculine plural form? Second question is, any difference grammatically here between 'those are' and 'they are'?
Yes, they are your children should be accepted, if the kids are of mixed gender. You can't distinguish between all boys and a mix in Hindi. As for the second question, I think 'Those' is supposed to refer to far away and 'they' to close by.