[Z]

I'd want to swap but I'd want to keep in contact with the other family and we could help each other through the inevitable upset and difficulties in adapting to the change... I'd make sure my child referred to them as auntie/uncle when they were old enough to walk and talk and explain the situation to them when they're older.

I absolutely wouldn't go for it. I would never want to set myself up for a fall like that, it hurts a lot to be cheated on and I think if you really loved that person it would hurt even more and would be very difficult to get over.