I think the fact that I wasn't quite done with their papers was a good thing..
I had time to talk with both Ethics classes about what was coming -- before anybody saw their grade.
A few students even mentioned the helpful handout in the writing center -- and others said they'd used the link to a good college website on citation. The message to the others was pretty clear, 'we figured out how to do this and you can too'.
They'll have just under a month to do the revision. I made it clear that the revision was to be for citations only.
I also told them that this was the standard in academic writing and that they'd better learn it now than in a class where the prof calls it plagiarism and gives them an F... or when someone doesn't permit a revision -- like I was considering. I told them I thought it would be unethical of me to just pass their papers along -- and that I didn't like the idea of dealing with their papers again... but, I thought it was the right thing to do.
We'll see how they respond -- I got the 'stink eye' from a few -- and called one student on it... in kind of a joking manner, but she got the point and shaped up...
I'm sure that I'm going to adopt this policy from now on. I'm also going to round up an electronic copy of the writing center handout to include in every course -- and simply return any paper that doesn't meet basic academic standards.