Note that these steps are for integrated webcams only. If you have an external webcam, disabling it is easy -- unplug the USB cord that connects the camera to the computer, and hide the camera somewhere your kid won’t find it! (Just kidding. You can also use these steps to disable an external webcam, but you'll probably have better luck simply by removing the device.)
To begin, go to the Start menu on your desktop and click on "Control Panel."