If you have lots of time (or cheap labour?) on your hands...
...then iron them. Or perhaps best, if they're more than just the tiniest bit wet, do as Ross says and sun-dry them, and *then, just before* they're completely dry, iron them.
Paper irons pretty well, especially if it's just a little bit moist before you start. Not on the hottest temp a normal iron is capable of, but not on the lowest either, IIRC; somewhere a little bit above the middle of the range, I think.
Yes, if they're anything thicker than Aidan's six- or eight-page "My First Book"(*), that's a pretty Sisyphean job... So maybe you could figure out some appropriate (and in an ideal world, even paedagogic) bribe to get Duncan to do it?
HTH!
(*): Or whatever it's called -- and besides, that would be a different kind of problem altogether anyway, since those usually have thick cardboard pages, which would tend to warp and buckle much worse than paper, and probably even split up into separate layers.
