Comfort foods, like applesauce and some sliced fruit, pedialyte and pedialyte popsicles. Steer clear of dairy products if the kids are at all snotty, it will make it worse.
However, if there is diarrhea involved, some yogurt will help.
Influenza is a virus so there is nothing the doctor or you can do about it but make sure the kids stay hydrated and as comfortable as would be possible. Alternate doses of ibuprofen and tylenol every few hours will help tremendously. And don't forget most viruses take around 21 days before they are entirely eradicated by the body, so don't be surprised if the kids seem like they are still a little run down after the worst of it passes. Hang in there, it will pass!!
PS..if they aren't using the potty (to pee) at least a few times a day I would consider a trip to the ER...the vomiting will dehydrate them and the ER can start an IV to help.