You could try lots of things. Emergen-C packets are great for their varieties of vitamin C, and the fun-for-kids factor. Look up some general antiviral support measures. Goldenseal, Elderberry or Sambucol syrup. If you have any homeopathic aconite around, give some doses of it while you're figuring out what else to do. Cold or not, it's good for them to have the pox. I never got it as a kid (sat with both siblings when they had it, too) and I got it in my twenties.