Best content filtering software

I’ve just finished setting up the (hardware side of the) family computer and I want to set up some content filtering so that my kids can get very limited access to the internet.

At the moment, all they need is to be able to access sites that I have previously selected an vetted for them; they mustn’t be able to follow outbound links from those sites. Sounds overly restrictive, I know, but they are only aged 4 and 6 and they aren’t ready to browse/search yet; they just want to be able to get to www.bobthebuilder.com and the like.

I’m sure there must be quite a few offerings out there that will do this, but which is the best?

I’m also looking for a way to organise their (IE) favourites in a more friendly graphical way, but as I’m going to be building their bookmarks list, I might just knock out a local web page with linked pictures.