Say nothing – let them feel normal. I had a period of a few years between children and the best times were when there was noone trying to guess what was going on or trying to only say certain things.
Do try to be sensitive with babies and discussing baby things and how cute the kids look. There is alot of pain that you cannot take away regardless of how well meaning you are.
Ultimatly each person is different so what worked for me may not work for them.
there was a time I was unable to go to a bris or be in a room with other newborns