Libraries as such, are helping users exercise their fair use. So that's how libraries get implicated in fair use and teaching copyright. In fact, the job of libraries is to help their readers use their fair use rights under copyright. Libraries are drawn into this and become advocates for their users, not for themselves. I think that's an important distinction.
Libraries fill a supporting advocacy role, a role that defines what a librarian is.
I certainly don't think children need to be tied up in knots with all of these technicalities, but that their teachers need to understand what copyright means. Teachers have to know what they think about this. It's probably the latter. I don't think there's a great deal of awareness on the part of students or faculty of what the copyright law says. It is the role of the librarians to educate and inform users about copyright as and when we have that opportunity.