Shoutbox

You can get some basic internet filtering software in many computer shops, it doesn't need to be any of the expensive ones. McAfee do one that's a one off payment, no subscription and you can set it for appropriate filtering for ages, or just to filter only sites you don't want to access. Then you need a password to view it...it's main fault is that it can be disabled by ending the process, which many other internet filtering software products have safe guards against. So unless your brother is a complete n00b it is no good.

CyberPatrol (despite the crap name) has many safeguards to protect against tampering and ending the process, and can be set only to block specific sites that you wish blocked, however I just had a look at the subscription cost and it's around £17 a year...
Look on Google for other internet filtering software...but that's the safest way to make sure it works without complications.