Say you have a child who's allergic to peanuts. You decide to eliminate them from your household, do a top to bottom cleaning, and you're done. Right? Well, pretty much, sure.
But what if you have a child who is allergic to 10 things? Things you can't give up for any number of reasons. How do you avoid cross contamination then? How do you make eggs for your oldest child without killing your youngest?
Maybe you have separate pans and utensils you use to cook the allergenic foods? Or separate knives and chopping boards for each food? And you likely isolate the allergens in a cabinet or part of the fridge that your child can't reach (or knows not to). But beyond that, what can you do?
Here are links to some sites I found online that offer some good tips to avoid cross contamination when it comes to allergens:
CIA - Professional Chef Site focusing on food allergies