Old thread ahoy!
Saying that, I'd like to have some input.
My partners first child was bought a netboot for Christmas. She's 7. She's also home schooled. I went and put a copy of Edubuntu on it, and it's been absolutely brilliant.
Chrome and a parental control addon seem to be doing the trick regarding web blocking so far, and she's always monitored when she's on it (She's got links to the Disney website, Cbeebies site, and some other browser games thing.