My son's had croup twice (and my daughter never, despite her being older, and in daycare longer), he seems more prone for some reason, maybe a subtle structural difference? I'm grateful that for us, it's stayed mild and easy to treat at home. For him, treating colds promptly seemed to be the biggie, for us lots of vitamin C, to bowel tolerance for him, makes the course of colds/coughs/similar illnesses faster and milder. Now that he's not an infant, we make Aviva Romm's garlic lemonade (garlic, lemon juice, honey water), it is really tasty and drinking it warm feels really nice.