However, if (general) you don't have a kid with those kinds of allergies, you're probably not going to be nearly as vigilant or thorough because it's just not something you deal with or think about regularly.
My allergist told me that at an allergists' convention, his wife had gone into anaphylactic shock after she took a cracker that was on a lettuce leaf that had previously had shrimp lying on it. And of course her Epi-pen was upstairs in their hotel room. Fortunately, in a room full of allergists, there WERE people who were carrying Epi-pens. But that little bit of shrimp juice that soaked into the cracker was enough to have killed her.
Personally, I was a little surprised that shellfish would be served at an allergists' convention (considering how many people choose that specialty because of being allergic themselves). But apparently, whomever had planned the convention catering had not thought about it.
Who would have thought that the lettuce would be reused- and that it would retain enough shrimp juice to harm someone? But with that level of allergies in a CHILD, I would think that a parent would best assume that all surfaces ARE contaminated, rather than hoping others will police the environment and leave it allergen-clean.