Don't worry about your son. You couldn't stop him from being a Sox fan if you tried. My son was 10 years old in 1996 when the Yankees were winning the WS. I live in NY. I felt bad for my son because all of his friends were reveling in the Yankees while the Red Sox were steaming pile of s***. I told him that he could root for the Yankees, that he should have a good time with his friends and enjoy rooting for the Yankees. I told him that he didn't have to root for the Red Sox, because I did. I cautioned him that the Sox were certain to always break your heart. He looked at me and very seriously said "I can't root for the Yankees. I hate them." It was one of my proudest moments as a father. We shared the heart break of 2003, and my heart broke for the boy, but in 2004 we shared the "Ultimate " victory that made all the past suffering go away because it was so perfect.
So, don't sweat it. It might take years but the pink hats and the posers will eventually go away, the diehards will retake Fenway and this team will get back to concentrating on putting out a winning team.