J.C.
So your 2nd grader does not know you are sick, yet you are noticeably tired and losing weight? I hate to tell you this, but he knows, and if you have not sat with him and explained what is going on he will just be even more scared. I understand the desire to protect them from all bad things, but you can't protect him from this by pretending nothing is going on.
It was hard to find the right way to explain my husbands brain tumor and brain surgery to my children in a way that would not scare them while still allowing them to understand what was going on so they would not be scared by the not knowing, but I found a way, you will too. But until you have had a chance to sit with him and have that talk just politely tell the askers that you do not wish to discuss it now, or that you will talk with them about it later because you want to focus on having fun for the holidays.
Blessed Be