fenwickchic, lalaland covered it well. The only alternative I would suggest if you can't find or don't want to use permethrin (it is what I used when my birds had mites, I bought liquid concentrate and sprayed everyone down, and it work fabulously well, and fast) you can look for something Cynthia12 (and probably others) has suggested in the past - in the pet bird section there should be a spray bottle for mites and lice used on parrots/parakeets/finches, spritz a couple of times under each wing, around vent, and based on my own experience I'd spritz the head as well, I had a Silkie whose head was pretty badly infested. I think the pet bird spray is pyrethrin. Right now if I was you I would be way more concerned about making sure my birds were rid of the parasites quickly. You are right to worry. By the time you see a bird looking down it has been suffering in silence a lot longer. They are built to hide weakness, like most animals and birds.
Going forward, keeping a dust bath bowl available for them with wood ash, peat moss, dirt, etc. should work as a preventive. Stop beating yourself up, you have worked hard to keep your birds happy and well fed. Now you have learned as most of us have, the hard way, to pick up birds every few days and check for parasites. They come on silently and without warning.
Going forward, keeping a dust bath bowl available for them with wood ash, peat moss, dirt, etc. should work as a preventive. Stop beating yourself up, you have worked hard to keep your birds happy and well fed. Now you have learned as most of us have, the hard way, to pick up birds every few days and check for parasites. They come on silently and without warning.
Fun Fun... we weren't sure what she'd think but she was WAY excited. I'm afraid the younger 2 daughters are now trying to figure out if they can get a chicken tractor on the balcony of an apartment or dorm room. 
