This is where the big boy pants come in. Your thier dad and its your job to be there for them and part of that is keeping their sadness to a minimum
Jim, honey, this^^^. I know it's hard but forget your W, it's not about her anymore. It's about those precious kids. They are far too young to understand right now. But rest assured that someday they will figure it all out and what you want them to figure out is that you were the one who put them first.