Darwin - what an undertaking! I applaud you wholeheartedly! I'm a former shop teacher and always wanted to do something like this but couldn't due to liability, etc. I'm in hopes that even if it doesn't work out for a large group, you could at least get a few interested. It would be something that they will always remember and treasure.
If you are going to have them use "kits" - they'll have to do the woodwork to final fit the parts (if needed) as well as sand, etc. and apply finish to the stocks. Looking the entire process over, I am guessing that you want them to get an intro to ML, doing a project and having the satisfaction of having something when they are done, etc. Speaking from experience (for shop classes), you will have some who are "perfectionists" and some who will not be. You've worked with kids so you'll know what I mean when I say that the most important thing that they get out of it is "confidence" in themselves. I'm sure that they would find a project like this interesting and it opens up a whole list of topics that you can expand on from history to safe shooting to combining it with primitive camping, etc. At any rate, I think that I would have them finish the barrel, lock, etc. themselves. While maybe not 100% historically correct, cold blue is easy to do as is the use of Plum Brown. It would give the opportunity to teach lessons on metal work - polishing, preparation for finish, etc. and in the long run, wouldn't require much more than emery cloth (for a kit gun) to polish the metal up. I don't know what your time limits are for the project so I imagine that would have a lot to do with whether they have time to do the metal finishing or not. I'd also suggest that you approach the local lumberyards, etc. for maybe a contribution of sandpaper, stains, varnish, etc. as well as gun shops or suppliers who might be willing to donate cold blue, plum brown, etc. I know it is tough with the economy, but most places have a soft spot in their hearts for scouts, etc. Hopefully you can get some parents involved as it would be a nice way to give some "bonding" time along with the project. Just my 2 cents worth - I hope it works out for you and the kids as it sounds like a terrific idea. Good luck! Sincerely, Bedbug