Explaining closed communion to non-Catholics

My oldest son is getting ready for First Communion this Sunday. I believe my family will be attending. The question is how do I explain closed communion to my family without being offensive. I realize they may be offended either way (as I was before I converted) but how do I present it in a way that helps them understand and is the least offensive? What have been your experiences with this issue?

I think you could probably touch on the fact that this is Christ Himself that we are recieving in communion and not just a symbol as I suspect they believe (correct me if I'm wrong on this point) but probably don't go into that a huge amount. That would probably just start a heated discussion.
I think the best thing to bring up is the fact that by us recieving communion we are saying by our actions that we are in communion with each other. By being in communion with each other means that we believe fully all that Holy Mother Church teaches and that we fully consent to that teaching. Since your family is not Catholic, they obviously don't believe everything that we believe, so they would be in effect lying in their actions by recieving communion with us.
Of course, you would know the better way to word these points for your family, but I think this would probably be the best approach.

And.......a HUGE WOO HOO for you son on recieving his first Holy Communion!!!!!!!!

Let me second that WOO HOO!

Not that I have any great ideas, but... Will your sister be going? She will know that she cannot go up for communion, maybe you can ask for her help. If she were to do a reminder to your family then it might be easier on them. This way it is not coming from you so they won't get mad at you, and it is just a fact coming out from your sister, so they should not take much offense from her. Maybe she doesn't even have to say anything but can get out the missel and point to the paragraph that says welcome, but no communion. She could act as though she is just an interested reader.

I know that this is passing the buck, but that is what sisters are for. (Taking one for the team and all.) Of course this will only work if it is immediate family. If there are a lot of family and friends it might not work as well.

You could also say something to your Priest. He might be able to help.

Just some thoughts. Good Luck.

Terri