I fully understand your frustration, however, this setting relies on your school's Canvas administrators specifically to fix it (teachers can't).
The school's / program's Canvas admin who has access to the root-account level as an account admin will need to grant students access to generate a pairing code for an observer from the 'Permissions' tab. They are the only users that can perform that action. If it's not enabled, then nobody is able to generate a new pairing code.
However -- let me confirm. Your child is actively enrolled in at least one course as a student, right? If they are not actively in any courses, I don't think the option appears in their settings.