I agree with isolating them from the others. You can also teach them to sneeze and cough into the elbow - that's the new "cool" thing (advised by doctors) and it's much better than coughing into the hand which then is used to touch other things.
I disagree about all that bleach and lysol - they are really pretty toxic (especially the bleach) and terrible for the environment. Too much exposure causes damage to the person using it - I forget if it's liver or nerve damage, but my doctor told me this. Moreover, the doctors and scientists are saying that endless disinfecting (with usual cleaners and also antibacterial hand soaps) are actually killing off weaker bugs and allowing for the emergence of "super-bugs" - it's making the situation worse. If the kids had colds, those are viral infections - nothing antibacterial is going to work anyway, and there's nothing the doctor can give them (no antibiotics). Perhaps something at night to ease the coughing and congestion so they can sleep and get some rest would help, but that's it. If it's really bad, someone should listen to their lungs (pneumonia, asthma) and check for sinus infections, but that's a judgment call.
Regular vitamins don't work very well - only about 20% is absorbed and the rest passes out of your body. I've got a page from the Physician's Desk Reference that explains this and there's even an x-ray of undigested pills working their way through the intestinal system.
We used a comprehensive and balanced liquid nutritional supplement (powder you mix in liquid at the time you're taking it, so it's freshly made and doesn't degrade like premixed liquid supplements). It's patented (so it's safe, effective and unique), manufactured in the US, and easy to just drink up. No one's been sick in our family in years, including when the swine flu hit and every other infection, plus this insane spring allergy season was nothing for us. So it can be done, but not with anything you buy in the supermarket or health food store - those are usually just heavily marked-up mixes.
The only other thing you can do is not take those kids when they are so sick. They must have been miserable and probably wanted one of their parents and to be able to stay in their own home.