I never really had to have a talk with my boys. My Grandmother did most of that for me. She'd talk to the boys about those who had already passed, like my father. She would tell them stories about him and they would ask her questions like "Would he have liked me? Weren't you mad when he was killed? Weren't you sad? Will you die?" She answerwed all their questions, sometimes with a tear in her eye.
She talked about the pain when you loose someone , but the joy in knowing that when we pass, everyone who had gone before us will be waiting.
She told Brad once that even though she loved him more than a cat loves sweet cream, she would have to die. She told him to close his eyes and asked him if she was there. He said yes. She asked how he knew, he said because I hear you. She told him to go into the next room and was asked if she were still there. He said yes. She explained that when she was gone, she would still be there even if he couldn't see or hear her. She would continue in his heart.
She's gone now and we miss her, but she's really not that far away.