This sounds like it could be viral or bacterial in nature rather than an allergic reaction. Huzzah for Karen's recommendation of chamomile and mint tea. They can help soothe irritated tissues and improve enzymes needed for proper digestion. Plus they taste great anytime!
Home remedies for which you might have the ingredients at hand or readily available at a nearby store:
Chop a handful of red radishes, mix with 1 cup of cold milk and 1/2 teaspoon of cornstarch. Drink the mixture slowly. This natural remedy for diarrhea should stop the diarrhea within an hour. Repeat again in 4 hours, if required.
Mix the juice from raw ginger with raw unfiltered apple cider vinegar and sweeten with raw honey. Add water and have your children drink this frequently, sipping rather than gulping.
Grate some fresh carrots and add them to a soup with brown rice. The rice will help firm up the stools and the carrots and rice offer minerals which are depleted through watery stools.
Fresh blackberries and bananas help cure diarrhea. Eat in moderation to avoid constipation.
Hopefully you'll have the ingredients on hand for one or more of these remedies, and maybe tomorrow you can get more ingredients so you can offer them a variety of different curative foods. Let food be their medicine, and they will regain health quickly.