Pretty much just inevitable. Good news though, in about 5 years you will be completely immuned and will barely ever get sick!!! I do (with parental consent) provide vitamins for my daycare kids and really push the parents to give them at home. other than that, not much you can do as far as picking up sickness, just wash a lot and wipe the toys, keep "mouthers" toys seperate if possible. (I don't allow the older kids to play with the baby toys and vice versa) can't think of much else, just comes with the territory of newer daycare, you really have to build immunity and that just comes with time.
oh! I swear by airborne though, as soon as you feel cold symptoms, pop one tablet into 4-6 oz of water and drink. you have to catch it early though. good luck!