The Gimp, an open-source image editing application, has a nifty Auto White Balance feature that can fix such problems. It doesn’t actually correct the white balance; instead, it expands the range of red, green, and blue values to their maximum. Or if you use a Mac, GraphicConverter (shareware) has a white balance correction feature in which you choose a point that is supposed to be white and the application corrects the values. It’s trickier but more accurate than the Gimp’s feature.
Turns out iPhoto has a Temperature setting that seems to be designed as a white balance corrector, and was easiest to use for a novice. It’s got the “choose a white point” approach too, but that’s harder than I thought it would be. No batch change, but possible to set up a pretty efficient factory line. My family looks SO much healthier.