You'd need about 0,00001ASA material for a 2 month exposure with a regular pinhole camera... that just doesn't exist, unless you plan on using whatever Mr. Ničpce used for his first photo around 1820. With a very big pinhole camera with regular photographic paper (that would need exposure times of a few minutes in full daylight) and a x1000 ND-filter, you'd still only have about 1 day of exposure...
I used homemade ND-filters from exposed and developed negative film before. Just take out-of-focus photos of a white wall with perfect exposure, then +1, +2, +3, +4 and +5. 35mm film will do for this, but it should be very fine-grained... develop as usual and then test how dense it is by holding it in front of a light meter. That way you can see, how much light your "filters" absorb and find the right density. 10 stops is the minimum you'd need... I can do the math for you, if you're interested. These DIY-filters are not good for sharpness, though. A single piece might be ok, but stacking several for better effect, will make the picture way to blurry.
You also could take a photo of the solargraphic negatives on slide film (preferably with a large format camera) and enlarge that onto regular photographic paper. Or use positive paper for the solargraphs, photograph with negative film and enlarge (or contact print) that. It's a bit complex, but it should work. I don't know, if all that stuff with inter-positives (or negatives) might be to complicated for such a project with kids. I haven't tried it myself, so you'd need to experiment yourself before the official project.
I'd just do regular pinhole photography with positive paper. Negative paper works too, but seeing the "proper" image right away is probably better for understanding.
If you want to interest these kids in analog photography and darkroom work, anything too complicated will probably lead to "ehm, ok, I could've taken a better picture with my cellphone in a few seconds... this stuff is old and boring." Says me, who was a kid about a decade ago.
Another very fun thing (well, I loved it), I'd recommend, is making photograms. Just let them put some random stuff onto a piece of photographic paper, expose it with an enlarger and develop that. It's not what they'd imagine as photography, but it shows how stuff in the darkroom works and has that magic of seeing the image appear in the developement tray... also lets them do everything themself.
Last edited by moki; 05-17-2011 at 06:03 PM. Click to view previous post history.