get 'em back.
go to your kids computer and hit PRINT SCREEN.
then open up MS Paint, click Edit then PASTE.
Save as JPEG, open it up, and set that as the Desktop Background.
THEN just drag all the icon's on the desktop into a folder and move it onto the C: Drive. (just go to My Computer, C: and cut/paste it in there)
Your kid will freak out when he can't click anything.
It's a good 'un.
I can one-up you here.
1. Start as above, taking a screenshot of the desktop. Paste it in a graphics editor, then INVERT (it must be flipped NOT rotated to appear correctly) the image so it's upside down.
2. Save this and set it as the desktop background.
3. Hide their desktop icons (there's an actual option to hide the icons, so you don't need to move them to a folder).
4. Set the task bar to auto-hide, and reposition it to the TOP of the screen.
5. Invert the desktop (usually CTRL-ALT-Down Arrow, or do it from the Advanced options under the Display Settings depending on your monitor and video card).
6. Sit back and laugh.
You can complete this image by creating an inverted mouse pointer (inverting the desktop will make the mouse pointer look like it's upside down, so creating a special pointer will fix this).