It's not discrimination if it's got another basis -- like that the children aren't Muslim and there are families with a more suitable religious match.

Non-discrimination should not imply forced mixing. Would you put Muslim or Jewish children with a family that did not follow Halal or Kosher diet? Well, even though Christians don't have religious dietary restrictions that I know of, there may be other aspects of Muslim upbringing that contradict the beliefs of many Christian families, and these beliefs should be equally respected.