There is absolutely no way the children will be removed on the basis of what OP has said, unless there is a lot more to it. I’m very surprised actually that he was given supervised access only to the children.
When a woman leaves an abusive relationship, no matter how bad it was, she might find immediately afterwards she has support but it’s a bit like a bereavement: time goes on and people forget and get bored and move on and away. In 2016 you might be the heroic tigress moving her cubs away from a violent and unpredictable man. In 2017 you are a single mum on benefits and lonely to boot. This might sound harsh: it isn’t meant to. It’s how it is. The abusive relationship you were encouraged to leave becomes something that with hindsight doesn’t seem that bad.
A lot of women end up in abusive relationships time and time again. Some go back to the abuser. Many don’t, but start new relationships with someone who is pretty much the same. We all have tendencies, bad habits, inclinations, and some people have a very strong ‘pull’ towards these relationships due to childhood abuse a lot of the time (not always sexual abuse but frequently is.)
I do always wonder about friends who like the OP are keen to ‘help.’ No adverse inference on anybody who does. My parents died; my friends are my world and I’ll pull out the stops for them but that’s because they are my friends, not because I expect obedience or subservience in response.
Because going back to an abusive relationship might seem when put baldly a selfish act, but it’s not, is it? Not when you consider our ‘typical’ abused woman has had her head fucked around with so much that she doesn’t know what’s right or what’s wrong any more. Think Jaycee Lee Dugard, who stayed with her captors for years - didn’t need chains or ropes to keep her there, they’d got inside her head. That’s what they do. Turning that into something that’s ‘me, me, me’ - I gave you help, I put you in touch with WA, I even went to the police and this is how you repay me - moves the abusive relationship to the back of the queue and puts the ‘helper’ in the role of victim rather than the person being hit or raped. It makes the true victim just a thing that exists to either make them feel good (‘oh well done, you left’) or bad (‘bad woman, you went back after all I did for you’) and while I think some frustration is normal, having those feelings persistently is a bit demanding in terms of making your feelings the most important thing in the whole equation.
It’s a bit like that post on MN sob stories: don’t give more than you can afford to lose. But even that isn’t so straightforward because if you make someone feel that their feelings aren’t important, reducing something that could indeed be very dangerous to something that makes you feel bad is questionable and silly.
In other words, we aren’t the moral gatekeepers of our friends. If they cross what we deem to be a line we have a choice to withdraw the friendship. This may be such an example for OP. But I think we have to be very careful of offering friendship conditional on certain expectations being met, particularly to women who have a history of abusive relationships.