I'm so sorry you are experiencing such difficulties. Children's Services aren't much better here in the UK, but, under The Children Act, children are considered to be "at risk of significant harm" if they witness DV. Even though Child Services failed my SD when she was living with her alcoholic mother, they did remove her half brother after he witnessed mums boyfriend beating her up.
I know this doesn't help you, but it is considered harmful for children to witness DV. Keep fighting. And stay strong.