I wonder how skewed this number is in the US due to doctor's notes for (un-needed) school lunch exemptions, assuming the note got charted (which is basically mandatory with electronic records). Even when I was in school, (before allergies were cool) a large number of kids faked it for access to the alternative menu, or to be allowed to bring their own lunch and snacks. I suspect it's only gotten worse.

In the overall US population peanut appears to be the most common, 58% more prevalent. In children, milk is far and away more common, 220% more prevalent, but many milk allergic children outgrow the allergy.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4254585/