I went through this last year when my aunt was diagnosed with an always fatal, rapidly progressing disease. While we don't live near, my children were fond of her, especially my daughter. I told them truth as we found it out.
My children had a wide range of reactions with my daughter's being quite intense through those weeks, my older son's more matter of fact, and difficult child's with not much reaction at all. On the plus side my daughter has a strong faith and got comfort and assurance from there. She has a very merciful temperament and "felt" the sickness and death strongly. There were times when talking helped but there were also times when I cut her off from talking about it because I could see she was working herself up as a result.
