By not demonizing the parent I mean making not calling them ugly hateful names. There's no need to make the situation worse. You can still be honest and truthful without demonizing the WAS.
For example, I told my kids that their father was unhappy and wanted a divorce. That's not demonizing him, and it was telling the truth. I never told them D was okay. It's not okay and I would be very disappointed if they made this type of choice. I never told them it would be easy, or that life would be great. I told them it would be difficult and it would be hard, D isn't a good thing, but I loved them, and that I'd always be there for them, and we'd do our best with a difficult situation. Life can be hard, people sometimes make difficult and selfish choices. But we can't change that, and in spite of it we have to do what's best. I told them their father loves them. He truly does, but I pointed out he was unhappy with me and wanted a change in his life. This was not a lie....
However, my kids are older. They knew what was going on. They knew about OW and understood more than my words and actions. And because they are older I could share with them my experiences with step-parents and experiences I've heard about (the good, the bad, the games, control jealousy, etc...).
Regardless of all this, I do think it's a good idea to read books on this and get an idea of what it the healthiest way to do this with kids. I'm sure it isn't lying and glossing over things, but taking the anger and crazy emotions out and reassuring them that they still have your love and stability to depend on.
There is no arriving, ever. It is all a continual becoming.
