BoyZone.com is really really not about a boy band...
At 5yo, DS found a video, and so asked me "What's sex..."
So I he had his first "talk".
He wasn't very interested.
"What's violence ?"
Turns out that he was reading the back of the Curious George cartoon DVD, and it said "no sex or violence"
I don't have any sex hangups, so if DS did ask about fellatio, he'd get told. From what I observe terms like blow job are in common (if inaccurate) playground use much earlier than many parents would like to think.
All the nanny controls can be circumvented, trust me on this...
Currently DS is "guided" in his web access, and since I know lots of good, interesting sites he has little motivation to find his own.
That won't last forever.
Once they've decided to find something, then they will. I would bet money the 8-9 yo at your kids school already pass around "interesting" web site addresses.
You basically have two options.
1: Deny them unsupervised access to the computer, and that includes following a password discipline that many firms have difficulty enforcing on (allegedly) grown up staff.
Otherwise the kids will get your password, good chance they already have.
2: Educate them. That involves a sex talk, which is probably harder for many people than explaining the technology.