At my Tribunal I *was* represented, but it ended up me doing most (nearly all) the talking anyway. Most of it was them asking me questions, which I just answered honestly.
I think you will be absolutely fine, and they will listen to your son too. As he is at home with you that will really help as he can tell it like it is.
Good luck and don't worry about it too much. I wish I had known how easy it would be before I won my appeal - I would have not given it a second thought.