I think that because she has children, it's even more important to make sure he knows she will not accept this sort of behaviour. If he does it once and gets away with it, he'll do it again. And if he does it a few times, it will spill over onto the children.
Take action now, make it clear that you expect to be treated properly and will take action if you are not, and it will be better in the future.
I've spent years down the courts, and I can honestly say that I've never seen an extreme act of domestic violence that didn't have a long history of minor acts of violence or criminal behaviour leading up to it.
If you accept one blow, or one act of vandalism, there will be more.
