How to setup Guided Access in iOS 6 to shut off areas of the screen or to keep an app from closing
Once you've updated your device to iOS 6, click on Settings, then General. Next scroll down and click the new Accessibility menu.
Triple-Touch Home should be set to "Guided Access".
How to use Guided Access with Your Kids' Apps (or any app for that matter)
First, check the "Options" button in the lower right hand corner. Make sure that the options are set appropriately. We have the "Hardware Buttons" set to "Always OFF", with "Touch" and "Motion" set to "ON".
If you only want to make sure the app doesn't close accidentally, press "Start" in the upper right corner.
However most parents will want to make sure that kids are not opening ads, or changing an apps settings.
Press "Start" and hand the device back to your kiddo. To "Exit" Guided Access Mode, Triple-Click the Home button again and press "Cancel". You can then close out of the app as well.
One final note, this feature has been reported to "stick" occasionally in Guided Access mode. Just hold down the "Power" & "Home" buttons together for several seconds and the device will force quit.
Let us know in the comments section, if you've tried this and how it worked out.