I think less is more. Just tell them that you and her father, her teacher, her principal and she decided that this would be for the best.
You aren't responsible for their feelings about it and you don't have to answer questions that are inappropriate. Let them know that your dd still wants to be friends with their children. Be confident in what you've chosen for your family! You've clearly thought it through and are taking the best course of action you know! There is power in that confidence!