I don’t think we give our kids enough credit for being able to understand “adult” things when they are young. Your son’s ability to dissect the human condition of his grandmother is a testament to this. You are allowing him to see and because you are, he is seeing with his own eyes without being told it is something else. I’m sorry for what you have gone through and for your mother, but your son is learning some wonderful things by being present and by you allowing him to just be.