Well, I can speak on this. Since my stbx has been basically living a double life. Telling me one thing, begging to come back, blahblah, and telling the little girl the total oposite thing. That I'm the one bugging him...
I have thought many times, that she should know what a psycho she is dealing with. She is obviously too young and easily manipulated to see through the bs.
BUT...
On the other hand, I don't really think the op cares!! They know that the person is married, has kids, all that jazz, and they obviously don't care. Not the shining examples of morality, these people. i mean really, think about it. If they cared what the kids, or anyone else went through, they would not participate in this relationship.
Someone a long time ago, sorry can't remember who, told me that the OP is always "broken" in some way too. And it is true. So, trying to put reason in front of two broken people, or make them see what they have done, is fruitless...
Just my opinion, and I do understand exactly where you are coming from. You don't know how many times I have wanted to forward j's text messages to the little girl. Not because I want him back, just because I want her to know he is a liar. But, i haven't, and I won't.
"Success is the sum of small efforts, repeated day in and day out." Robert Collier
"One's best success often comes after their greatest disappointments." Henry Ward Beecher