If they ask, just reassure them that although you don't know why dad is doing what he is doing, YOU are not going anywhere and they can always depend on you to care for and love them. They just need to feel safe for now, and moms can do that for them all by themselves. They are kids, and need to enjoy life like kids do, and just feel normal and that it's okay. Don't beat yourself up. You are doing great. I think it's extremely powerful to start thinking of yourselves as "me and my kids". Let them see you powerful.