Christine,
What you are doing is so brave and being a true supportive friend. This will be a hard thing to do, no doubt. How old is your son? Keeping him out of the courtroom is probably a good idea anyway. I like the suggestions others have on what to do. If you have no other choice than keeping him in the room, maybe you could get a book on tape or something so he doesn't hear what is going on. I rent them from the library all the time and it is great for road trips.