A lot of them are. At Elementary Schools and where ever the children are.
Given the rash of sexual assaults and “consensual” acts involving teachers and students, I’m much more worried about the faculty than the janitors. In my local government school system, most of the custodial staff works the night shift, after the kids have gone for the day.
On the other hand, there are plenty of teachers—many of them female—who are cruising their junior high classes for sex partners.