I was divorced with a small child...my now husband was divorced with 2 small children.
My first husband passed away in 1985, but we were good friends AFTER the divorce and his family is still friendly with me. He would come to Mother's during holidays to pick David up and eat or whatever right along with Dennis and me.
Hubby's ex and I get along. She has been here in the summers bringing grandchildren home or whatever....she's drank coffee, Pepsi's at our house.
I attended both step-children's graduation with their Dad. I was the only one at the daughter's wedding other than the preacher and his wife.
Letting the kids grow up together made them much closer. My son has even spent the night at the step-children's Mom's house. (Boy...that's a loaded one!)
I have to say that I'm lucky in that department and getting along with the ex.