That's where my concern is. He'll see what appears to be a healthy cat being killed. By me. :-(
Thats exactly why I would take the cat now and not make a big thing of it until afterwards. My son and I had a little "funeral ceremony" to commemorate the passing of one of his friends. Thats probably all a 6 year old can wrap their minds around at this point. They trust their parents still and only know they will miss their friend.
Sherry