Android :: Write An App To Block Specific Webisites On Droid?

I'm considering writing an internet filter app for Android which would allow parents to block objectionable web sites on their children's phones. I'm assuming this would also be useful on GoogleTV when it comes out. How would I even start? Is it possible to block access to specific sites without requiring the user to root their phone?

I'm guessing I could do it with iptables, but that would probably require a rooted phone.

Edit:

If the phone was rooted, how would one go about doing this? Are ip tables the way to go or is there a better way?