My prayers go out to you and your littles one. I have been there and I understand. Here are somethings I did to help my daughter with everything. She was a little over 2 when we separated.
1.) Books - there are some great books out there about divorce. I read them to her. Please read them first to make sure they say what you want them to say. I found one that I thought I would like but I just skimmed it and didn't read it. My mistake. It talked about things not being her fault and a few things that might affect an older child but not mine. She didn't have these feelings so I didn't want to give them to her. I liked the book "momma bear and papa bears divorce" It is very simple and good.
2.) Have them go to a counselor. It might be very helpful in helping you understand how to help them. A counselor for yourself is great as well. I hated the idea of asking for help and going to a "shrink"....I am grateful I did and my counselor helped me tremendously.
3.) Always be positive and upbeat in front of the kids and their father. It is so hard and I hate putting on a smile. I forced it alot at first. After a while it becomes natural and we actually started getting along better. Remember kids hear everythign even when you think they are not listening.
Good luck. If I can help, please send me a private message. This stage of your life sucks. I know for me I am much happier now than I was before. I hope the same for you.