Fortunately, they have a template email you can send to them:

> Copy this e-mail and send it to a friend, your ceo or your company webmaster.

> Dear www.notfound.org,

> In the European Union alone, thousands of children are still missing. They run away from conflicts at home, are the victims of parental abductions, disappear after having travelled across the EU alone, or are abducted by criminals. But there is a way you can help, namely by installing the Notfound application. By doing this, automatically, a picture of a missing child will be posted on every 404 page of your website. This is how you can help Child Focus spread a maximum number of photos and help all missing children find their way home.

> Discover the application on www.notfound.org.

lol I will send them one :D

Actually their real 404 page, e.g. http://notfound.org/something.html or http://notfound.org/404 or http://notfound.org/bla.xml do display children.

What you happened to stumble upon was an existing page called 404.html, which of course is a bit funny.

This one does: http://notfound.org/somepagethatdoesntexist