Originally Posted by
LexieCat 
I think having your sister take him is a great idea.
I also think sending flowers with a nice note would be a kind gesture to let them know they are in your thoughts. You can explain to your son that as much as you loved grandpa, you don't want to upset anyone who might wonder why you are there. He's getting old enough to understand that sometimes you have to think of others' feelings in deciding how best to act in a situation like this.
Totally agree with what Lexie said.
My FIL just passed away a week ago today. My son is 7 and he attended the services on Friday. My situation is a little different in that XAH and I have only been divorced for 2 months and I've remained close with them. I think being at the funeral helped my son to understand his Grandpa is gone. He drew a picture and wrote a note to leave in the casket and got to say his goodbye. I know it meant a lot to my MIL and XAH that he was there. Seeing the military honors, flag folding, etc. at the burial also made him really proud of Grandpa. I think he'll always remember that.
Again, my heartfelt condolences. Not an easy thing to go through at any age.