M.F.
Hi N.,
I'm so sorry you are experiencing this painful situation. I worked for a hospice in Ohio a while back and we always counseled parents to talk to their children honestly about death. I agree with Denise that you should not use euphemisms - they will only confuse your son. Explain that Grandaddy is very sick and it might make him tired, etc. Simple, clear explanations are the best. After your father dies, you can tell your son that Grandaddy has died which means his body stopped working. There are some excellent books about death for children that explain how all living things eventually die. Bear's Last Journey is a really good book. Is your father in hospice care? If so, contact the social worker for resources. Your son may need lots of reassurance that you are not sick, etc. Or maybe not...let him guide you with his questions. It's okay to say, "I don't know."
I hope this helps a bit. Many blessings to you. Take care of yourself.
M.