I have to chime in a little here too. My kids are older than yours and are for the most part aware of what is/was going on. One thing I have heard from them, individually and on different occasions, is that their dad (and his new wife) bad-mouth and belittle me, and that really bothers them. I have tried to stay away from saying things about him or his new wife. If asked I have answered their questions factually and tried not to include opinion or judgment. A direct effect of that is that my kids have been able to draw their own conclusions on what has happened and I believe they respect me more for having taken the high road. when you belittle their mom, you are in their eyes belittling them as well, because they are a part of her as well as a part of you. They can love her without loving you less, and they will love her as their mom even if they grow to disagree with her choices and actions. Be the person that you want them to grow to be; strong, caring, non-judgmental.
"You can't stop the waves, but you can learn to surf." Jon Kabat-Zinn