In the absence of any software...start here...
The best "bit of software" is your own eyes
![Wink](/images/smilies/icon_wink.gif)
Don't let him near your computer without you standing over him...especially if he is young and immature, which appears to be the case.
Next option: set up your system to work under login orders only..i.e. you must login to access anything...especially your browser settings...crank them up to the top levels from the "tools" button.