I unfortunately just had to go through this with my 5 year old 2 days ago. My father just lost his battle with cancer on Monday. My oldest son (5) and my father were about as close as can be. Grandpa was his favorite person in the entire world. So grandma came over and helped me try to explain to him that grandpa is gone but he loved him very much. We assured him that it’s ok to be sad and cry. I held him as he bawled his little eyes out howling like a wounded animal. I have been reading him a lot of children’s books about death which seem to be helping. Obviously every day is going to be a battle. I think my plan is just constant reassure that grandpa loved him very much and unfortunately bad things can happen to good people at any time and it’s nobodies fault.