How can I force another user to sign out?

I'm the Admin user on my Mac mini but sometimes other family members use the Mac mini too with their own user/profile. Sometimes they forget to logout though. I don't know their logins so I can't switch user and then logout for them. And even if I did know their logins, that seems like more steps than it should be. With me being the admin, surely there's something I can click to force them to logout without my having to switch users.