When my mil passed away we made the mistake of not really talking to dd1 about where nanna was all we said was that she had passed away and was no longer here and watched us from the sky, (we don't believe in heaven but dd liked to think she was flying to the moon) we didnt take her to the funeral or visit the grave as we thought at 4 that she was too young instead it caused fear and anxiety as she worried about it all. It was about 18 mths later that I finally realized why she was upset snd anxious she was scared something would happen to us. So we explained where nanna was buried and visited the grave. She took a drawing and was happy to see where nanna was. The anxiety definitely improved. I think with your ds be honest and answer any questions he has and talk about the grave and ask if he wants to go,