I wasn't in the room. I heard them arguing, then a sound like someone falling against furniture and DD cried out. I sent DS straight to his room because we all needed space at that moment. DD said she was pushed; DS said he was leaving the room, pushed her with his shoulder and she "over dramatically" jumped backwards and fell.
Their father was (is) EA, that's why I left. I don't want my DS to think this is OK, but I don't want to imagine he's already like his dad, either.
So how do I deal with this, and is he likely to regret what he did?