Well, this is hard. No way around that. I told my kids that adults sometimes have problems they can't work out. We both loved them very much. it was not their fault and there was nothing they could/should do now or do differently. It was adult issues and I did not answer specific questions (which were actually very few and far between) because I wasn't going to paint their dad in a bad light. I repeatedly assured them that I loved them very much, that would never change, I would always be there for them no matter what, etc. I assured them that i was making the best possible decisions for all of us (which they disagreed with). We also had to move and I chose to move to a different town and that was hard on them. They were 3yo, 3yo, 8yo, 10yo at the time.
Their dad was not as kind. He repeatedly told them it was my fault, I was making him leave, wouldn't let him live with us. The kids couldn't go visit him because it was mom's fault that she wouldn't give him money so he couldn't eat and couldn't feed them. I was taking the kids to counseling and so he'd say that I didn't love the family because I wouldn't go to counseling with him. i was selfish blah blah blah. It was a nightmare to be honest and I am ashamed that I was not strong enough and clear enough at that point to keep them away from him. They were extremely mad at me, especially the 8yo (now 10yo). There was a year of crying, anger, huge meltdowns, rages. I left a very toxic relationship and a home environment that was subtly very toxic and instead of peace and calm my house had an all time high of fighting and chaos. It was a rough year. But - kids figure things out. I have never said a bad word about their dad but they no longer think I'm the devil either. They get it because I'm still here, I did what I said - and he isn't hear and didn't do anything he said. The older one especially see's this (and was able to see it more in the beginning). Most of that has subsided but I just signed the older one's up for individual counseling and we'll have a few family sessions as well. They are not close with each other. The big blow outs are gone but they bicker endlessly - more then normal - and that bothers me a little. I see them cry about things that I know are related to their dad. I think the 10yo still has a lot of confusion and anger over the divorce and the lack of a dad in his life. His anger goes into the world, the other one withdraws. I'm not sure what the little one's think. It is a new normal for them and we'll have to address issues that come up as they get older I suppose.
ETA: There are a couple of good books I got. I'll post the titles when I get home if you'd like.