C.,
My aunt and uncle both died unexpectedly in the same year. I was 7 at the time, and I went to the wakes and funerals. It did not have any "bad" consequences. Death is a part of life and children need to learn about it without it being all hush-hush - that just heightens the fear factor, I believe.
When I was in fourth grade, a schoolmate a year older died in a motorcycle accident. I didn't go to that funeral and have always wished that I had. It didn't seem real for a long time that Kevin was gone.
As for reminding the deceased's mother of what she has lost, She won't need any reminding. She will think about her son for the rest of her life, every day, and will at times want to talk about him and share both her grief and her wonderful memories. Don't make the topic taboo, you can't "remind" her about her son. Just follow her lead. That will help her the most.
I think the kids should go IF THEY WANT TO. Don't force the issue either way.
Good luck and my condolences on your friend's - and your - loss.
Would you let us know what happens and how it goes?