assuming he deleted the history
and assuming your using XP
click start
click search
click pictures, music or video
tick pictures and photos
click advanced options
click more advanced options
tick search system folders and hidden folders
this may take time depending on the amount of files on your pc
click search
let it continue til its done
then go to the top and click where it says 'size'
this will list them in size order
(basically you want the smallest ones at the top)
now go to the top left and click 'view'
then 'thumbnails'
you should now see all the images on your pc including all the little images and buttons that are used on the web pages
(sorry i cant remember the short way)
if you find something that looks like it came from a porn site
then right click on it and click properties
it will tell you the websit it came from
but remember he's growing up and its natural either get a netnanny program or change the settings on your search engine
dont have a go ... if you must say something then advise that viruses can kill the pc and they can come from porn