K.F.
I don't know what your beliefs are, but when our very close next door neighbor died, we just really told our 3 year old the truth. We told her that "Gramma Dee was really sick and her body was getting too tired so God decided that it was time for her to go live with him up in heaven. Now she doesn't have to be on oxygen and her body doesn't hurt anymore. We will miss her now that she is gone, but we will see her in heaven some day." She really did grasp it. The very next day it was raining and she asked me if Gramma Dee was helping God make it rain lol. Everytime she sees a dead bug or a dead animal or something on the road , or if she hears of someone who died, she will say "don't worry, we will miss them now, but we will see them in heaven".
As far as the viewing part, I explained that her body will be there for people to say goodbye too, but her spirit is up with God. She was still scared and wouldn't look at it. When she was 18 months old her Great Grandfather died, and viewing the body didn't phase her. Just be there to comfort her, I guess.
So sorry for your loss and good luck to you!!