You can google Michelle wiener Davis on you tube on what to tell the kids... she disagrees with the United front and called it a “flat out lie”. She has a nice way of wording things though. I really agree with her on this.
I chose to not lie to my son who is now 8 but he was 4 at the time. He asks me questions about who wanted the divorce and I told him that his father did. And that mommy believes in only divorcing someone if the other person did something really bad. Like hitting someone.
I do not want my son to think it’s OK to leave a marriage with a young child without working on it. I do not want him following in his foot steps. My ex mil lied to my ex about how his dad left them (his dad eventually came back when he was young) but he thought his dad ignoring them and taking separate vacations was normal. She Told him stories about how he was out provided. To my knowledge, my ex still doesn’t know the truth. I think it really messed him up. I feel like normalizing dysfunction (which is what ex mil did) really messes a person up. My ex ended up living this weird secret double life.
I do make sure to tell son that his daddy and I both love him. That his daddy left me and not him. And I tell him that his daddy left because he has problems. (His dad is a high functioning addict that depleted marital funds for years)
For what it's worth, I did not lie about the situation. I told them the truth (that I didn't want the D), but I also said that both of us were responsible for the breakdown of the marriage. I owned up to my mistakes. I told them that we both love them very much and that we'll have a great life and got them excited about the new situation. Telling them the truth did not do them harm. They are adjusting well. If you do tell them the truth, then I think it's VERY important not to then tear down there mother (or father). My motto is "tell the truth but stay classy."