I too am worried about your motivation here.
I worry you might be manifesting your jealousy and mixed feelings towards your ex into this need you have to warn OW against him.
Speaking from the other side, when I started seeing my OH, I received a bunch of erratic messages on social media from his ex, explaining (in graphic detail) how abusive he was, and how she was "only trying to warn me, for my sake". Cue me being very conflicted, thinking surely no woman would say thing stuff without justification, but it didn't fit in with the man I (albeit briefly) knew. It is a little different though, because although they had a child together they had been split up for over a year before I came along.
We have now been together years, and it's very clear that she was lying, and simply didn't want OH to be with me. I'm not saying that's what your doing, but it became quite clear that she would never let this narrative go. It is still what she spouts today (but has taken on many, many variations). And I genuinely think sometimes that she has convinced herself it's the truth.
My point is, and this sounds very blunt and horrible, considering what you feel you've been through, but they had an unhappy relationship. He was only with her because she immediately got pregnant, they were very young, and she has clearly twisted the outcomes of having an unhappy relationship into what she now labels as abuse. She never wanted to protect me from him, despite her constant insistence and becamse quite obsessed with me and with my relationship with OH. I'm telling you this because, like some other posters, I feel like there is something going on the surface, and can't help but feel you aren't being entirely honest with yourself.
If I were you, I would let her come to her own conclusion, if he has never been harmful to your kids. I would move on with your life and not dwell on his life or relationships. Good luck 