hi all,
sorry to hear all your little ones are going through such discomfort. As previously mentioned, if the fever is lasting for more than a 1-2 days, you should bring them to the doctor as a fever is a symptom of something else going wrong not the illness itself.
In terms of how long it can last, my son has been through high fevers lasting up to 5 days before it breaks (whenever he has a fever, it was never mild, always a 39 degree plus almost 40 degree fever!) so do prepare yourself.
In terms of food, fluid is the most important thing so give them whatever they can keep down - water, very diluted fruit juice with water, honey water etc, if they can keep down their milk that is good but it's not essential. In terms of food, the easier to digest the better (generally forget protein and anything with oil in it) - plain porridge, plain toast, water biscuits (no oil or butter), steamed pureed pear or apple.....
Another point, if you are sponging them down when they have a very high fever, do not use cold water (among other things it constricts the blood vessels causing a higher temp) but tepid water, the motion in itself cools the body down. Same for using a damp towel on their forehead or armpits etc, use tepid water.
good luck!