Your son reset your desktop resolution and color settings.
Right-click the desktop, select Properties. Hit the Settings tab. There should be a little slider dial--use that to adjust your desktop resolution to what it was set to before. Most likely it was 1024x768.
After that, there should be a drop-down box to the right of that slider dial. Click it and select "Highest (32 bit)" if it's available, or "Medium (16 bit)" if not. Hit Apply and your settings will go back to normal.
If everything still looks too big, go back to the slider dial and adjust it to the right by one or two notches. If it looks too small, adjust it to the left by one notch.
My kingdom for an Apply button ....