I've given my ducks Pedialyte after a fox attack (recommended by a decades seasoned duck owner) the plain (no colors or flavors added) and they did fine with itI agree - look at the poop. Keep up with the water and food, and if you can get charcoal, it would probably help things along.
I don't think they can get the flu.
Do you have poultry vitamins?
Question for others - I recall someone saying pedialyte is usable in a pinch? mustangluvrjen, don't give them that unless someone for sure confirms it. If you have poultry vitamins, that would be a good idea.
Have you been giving them grit at all yet?
