When you help your children (I know, you just couldn't resist.), please think about whether you want them to finish the homework, or learn how to do the homework. If you just want to help them finish the homework, stop right there, and let them struggle. May be they can learn something from their struggling. If you want them to learn how to do it, learn how to teach first.
Facts of Life: Those who wrote math text and teach math are not math experts. They are teaching experts. Their math may not be right.