Rick,

I have just about no experience at actually doing this kind of thing, so feel free to ignore me completely, but is seems to me like some of the answer to your query depends a bit on whether you look at your performance as entertainment or education. Of course, it will be some of each. From what I have heard of you I don't think you need to worry about the entertainment aspect. It sounds to me like the teacher who is hiring you is looking for the history of protest. That's good because I have always felt that there is a lot of history to be learned from folk music. It's bad because the subject is so broad.
Some of the songs you mentioned may not have the vitality for you that they once did, but they are still good songs. I think that to a degree you have to rely on the quality of the material to get the kids interested. Your commitment to the ideals in the song are probably less important than your commitment to the song. (As an example I sing lots of Christian music without beleiving in or even thinking about the words. It is rare that I will refuse to sing one of these songs because of the words as long as it's good music.)
I also think that it is a good idea to give some thought to why these songs were once very meaningful to you but aren't anymore. It's probably because the context of the song is in the past and you (as well as the rest of the world) have moved on. I think it would be useful to talk to the kids about that aspect of protest. I think that the kids will find your own experience to be interesting.
This has been a very interesting topic for me to think about. Thanks for bringing it up.