Doreen,
My surgery was a lot different from your husband's, but I can certainly relate to the issue with your 6-year old. I am also 42 and have two children, a 7-year old and a 6-month old.
I have found the best thing with my 7-year old was honesty. We just always discussed with her what was happening. Not sure how well your 6-year old can read yet, but writing to her before I could talk again really helped. Also, if it's any consolation at all, I can see her "healing" as I heal. It's like, the more she sees me return to the Mom I was before the surgery, the better.
Kids are so flexible. Just keep the lines of communication open and encourage him to ask anything he wants. Also, if you don't see that working and he seems to be withdrawing, there are counselors who specialize in dealing with the family members of cancer patients.
So sorry your family is dealing with this.
Jennifer