Yes the family needs to know because the changes do effect their child. But at the same time the details are private. It is sufficient to say oh just wanted to let you know that as of whatever date little XXX will be leaving care and we will have a new friend joining us. Then I would just go on and talk about the new friend as in their age, sex etc and make it all about what will be and not what was. Chances are the family is aware of things that were going on to some extent even if we don't realize how much they were learning and will understand without needing details. If they press then just say that child XXX parents and you feel that he would do better in a different environment and leave it at that. If pressed more then just tell them that just as you would not talk to other parents about their child you can't talk to this parent about the child that is leaving. They should be grateful to hear that. Again the emphasis of the news is about welcoming the new child and just closing the door on the old family with everyone.