You don't mention which OS you're using, but this works for 95, 98 and will probably work for you.
First, right click your desktop and select REFRESH. I doubt if that works...but might get the icons in a position you can use them.
Reboot your machine and enter SAFE MODE (95 used the F5 key, 98 uses the F8 key). As your machine boots, watch for "Loading Window XX". You'll want to hit the F5 or F8 key at that point. This is pretty quick, so you might have to try it a time or two. You should then see a boot menu...select SAFE MODE. This will start the computer with a minimum of drivers and, if your machine does what mine does, it'll start in 640x480 resolution (which is what you may be in now, BTW). Then, go to start-settings-control panel-display (or, just right click your desktop and select PROPERTIES) and click on the APPEARANCE tab. You can resize your icons and font there. To do what you describe, he had to change several settings. Icon size should be 32 or so....the font should be 8 or 10 regular (no Bold or Italics). Then click APPLY.
You might also want to click on the SETTINGS tab and see what's there too. I suggest you set the RESOLUTION at 800x600. Then click APPLY and OK.
Then reboot your computer and let it load normally.
Assuming your son just made changes in the settings, this should correct your problem.
If it doesn't correct your problem, got to START-SETTINGS-CONTROL PANEL-ACCESSIBILITY. I didn't load this on my machine, but it seems to me (when I did have it loaded a while back) that there are settings there for the folks who with really poor vision. One of those settings may have been selected.