well done. When XH first walked out for a few days, I told DD that he was working. She was only 4 and accepted it. When he left again 6 weeks later, and it was more permanent, I told him that he had to tell her that he was leaving. I was in a right state, as it had come out of the blue again, making love to me one day, walking out the next.....
anyway, my point is, that I was very upset, crying, and in no state to see what he was doing. I was in absolute pieces and DD was upset too.
He took DD into another room and told her that he was going to live somewhere else. I have since been told that he told her that I had made him leave.... She tried to pack a little bag and go with him. :(
So you need to be strong and Yes, you need to be there when he does it, so that you can know what has been said. I didn't get that chance and I regret it as he could have said anything to her. It was his decision to go, yet he still had to make it seem to her like it was my fault.
Don't find yourself in that position.