If they are over 12 years old, they can try Cold FX, sold at some stores/pharmacies, etc., but I am not sure they sell it in the USA...
If under 12 years old, a combination of zinc, ecchinacea, and vitamin C can help - sunkist makes something that happens to have those 3 ingredients in it... little chewable tabs. We took those - my 5 year old took 3 a day, and our 11 year old took 4-5 in a day, when they were sick prior to our trip. It seemed to help a bit. I would also try Vicks vaporub on their chest as a night time decongestant - it also helps with coughs.
GOOD LUCK!!!! I really feel for you, as no one wants to be sick!
If any of your kids are prone to ear infections though, I would take them in to see the Dr., just to be safe, as they can look at their ears to see if an infection is brewing.
Please keep us posted!