TL/DR: When I'm speaking in Japanese among coworkers, I generally use -kun for boys and -san girls or when addressing a student. Why is the owner of the eikaiwa I work for correcting me when I use -kun for elementary and preschool boys at our school?
I use Japanese considerably between coworkers, and while I'm still learning (working on N1), I'm pretty sure I understand when to use -san and -kun. I also avoid using -chan, especially when speaking about students between two teachers.
As I understand it, -san can be used with both boys and girls, but in practice, I hear most teachers using -san for girls. I'm know there are exceptions to this rule as -san is a polite form, but from my observations of Japanese professionals speaking to their students, -san is used predominantly for girls. For boys, I typically hear teachers (particularly at my elementary school and private kindergarten) using -kun all the time. I'm sure there are exceptions, but even my JTE is on the phone with his student (like when his student is out sick), he's referring to the student as ~kun.
So why is the owner of the eikaiwa I work for correcting me when I use -kun for elementary and preschool aged boys at our school? I can't seem to wrap my head around it. She corrects everyone, and even some of the Japanese teachers find it odd.
by T1DinJP