According to this article by the well-meaning Dr. JJ Levenstein, to keep your kids healthy you just need to avoid indoor areas, cover mouths and wash hands, surround yourself with healthy people, disinfect surfaces and keep sick kids at home.
Wow. OK, that list is virually impossible to follow. Avoid indoor areas? I'm guessing JJ lives closer to the equator than I do, and possibly does not send kids to the germ-incubator called school, and I would love to disinfect all the surfaces that my kids touch but I am too busy doing laundry and cooking and cruising online, and yes, I try and keep my sick kids at home but they have siblings and those siblings are not on quarantine everytime someone gets sick (no one would ever leave the house) and I might go crazy. So, my kids are going to get sick, and your kids are going to get sick. And once in a while, you get to enjoy having a sick day because it means you get to lie around on the couch and watch movies and drink hot lemon and honey. And other times, you are up all night cleaning up vomit and then spend the whole day -- cleaning up vomit. And sometimes it is a mixture of the two.
The real question isn't how to keep your kids healthy because we all do the best we can. The question is what to do when you have one kid who is sick because the liklihood is that your other kids are probably incubating the germ too. There is an etiquette involved when it comes to playdates. It is called advanced notice -- advanced notice does not mean that you tell the parent when they are standing at the door with their child ready to come into a house that looks like the Exorcist had been filmed in one of the bedrooms. And conversely, it does not mean complaining about your other child's illness when you have brought your child to their friend's door. It means phoning the friend as soon as the barf hits the floor or the fever registers on the thermometer in any of your kids.
I have noticed that as my kids get older and their parents get more worn in (or is it worn out?) that they don't care if you send over a kids who has a sick sibling. But if they are parents of one child, or of toddlers then you can probably forget the playdate. I often accept siblings of sick kids, but I don't usually send my kids over to a house with a sick child in it. (Unless it is an emergency like I really want to go Boxing Day shopping which is what happened last week. I dropped my kids at my sister's house even though her son was sick. And guess what the kids are fine, and I got sick.)