While some universities offer tuition waivers, that is not universal, even in the United States -- and where it is available, it is usually a perk offered to all full time staff and faculty, not just tenured faculty.
For example, I have been employed at three universities in Michigan:
- At Oakland University, children of all full-time staff or faculty get full tuition if they are admitted to, and enrolled full-time in, any degree-granting program.
- At Michigan State University, children of all full-time staff or faculty get a 50% tuition courtesy if they are admitted to, and enrolled full-time, a first undergraduate program. (In other words they cannot use this to get a discount on a second Bachelors degree or a graduate degree.)
- At the University of Michigan, there is no tuition benefit at all.
Other perks that full-time staff and instructional faculty may get (depending on the university and department) include a computer, office space, retirement (often including a 2-to-1 match in a tax-deferred 403(b) retirement fund up to some maximum), and a generous health care package. But again, these same perks are (often) not restricted to tenured faculty.