Raliced - this is so tough, but I don't see how it's your job to make their Dad smell like a rose. Sure you don't need to slate him in any way and it's so difficult for a 6 year old to understand the situation, but I think you're handling it all with such grace and dignity.
If he wants the kids not to think bad of him then I think it's his job to do that. Could you maybe ask your D to speak to her Dad about his new living arrangements, and you could maybe explain how it was his choice and not yours? What he's done is not good for the kids, he's only thinking about himself, so let him deal with the consequences. You can just be there to comfort the kids, which I know you already do.
Me - 44 Husband - 47 D20, S18 BD - Aug 2013 Moved out - Jan 2014 OW discovered Jan 2014