Calling names

Every boy in my kindergarten class is named John and every girl is named Joan.
The other five classes are the same.
We check with the other schools in the district and they are reporting the same thing.
You’d think someone would have noticed this with the birth certificates, but nobody noticed a pattern or raised an alarm.
Normal name distribution in the district, normal migration patterns for a developed country.
One boy’s eyes flash blue for a moment.
Then the others. They all smile.
Where did these kids come from?
And where did all of the normal kids go?