E.H.
Okay, I was 23 yr when my dad died suddenly and I am a girl not a 12yrs boy but I think that some thing that sticks out to me the most during that time was the friends that were there for me. Made me laugh, treated me "normal", and gave an escape from thinking about it. Sometimes it feels bad in the beginning to feel good. Playing with him. Just hanging out with a movie. Invite him over and away from thinking about it all. Giving an escape from all of it is helpful. He knows you know, but not talking about it could be a big help for a little guy (for anyone). Follow his lead, if he wants to talk, cry, whatever, just be there and explain to your son that too. That is giving your son the chance to learn a life lesson about being a good friend during this time for the future when he faces this again.