How can you force close another user's active login?

Here's the situation: I'm administrator on my machine. My girlfriend's boy has his own standard profile, but he has a password.  I use parental controls to lock him out after 9pm.

Now, at 9pm, Windows 7 (Home Premium 64 bit, if that matters) just does that annoying "fast switching" thing, taking him back to the main login page where the list of users is given. But it doesn't log him out. His profile is still logged in, and all the apps he was using are still running. That means if he was watching a video, it doesn't stop! The other night, I logged in after him and was forced to listen to Glee!  Glee!! Obviously this was unacceptable.

As an administrator, I should be able to force close all active logins, right? That seems like a no-brainer to me. Yet I couldn't figure out how to do it. Eventually I just rebooted.

Desperately awaiting good advice here.  Thanks!