[Billfred]

The internet's changed a bit since I was ten*, so personal experience isn't much use here.

Honestly, the best way to keep them off the shady side of the internet is to watch their screen whenever possible. Of course, that doesn't mean you have to be physically in the room; a utility like VNC would let you monitor (and control, if you desire) their computer from just about anywhere in the world with a decent internet connection.

When it comes to blocking, probably the easiest way to handle the decision is to only let through the squeaky-clean sites; sites like YouTube would probably be better off blocked until you override it.

Technical solutions will depend on other things. What operating system and security software does your wife's computer run? Is separate hardware or software for them an option? I've had good luck with parental controls on a Mac (and that's in the harshest operating environment out there, a college computer lab), while some might advocate a Linux live CD to help keep any errant clicks onto "500 FREE MOUSE POINTERS!!" from doing actual damage. But if the folks concerned are all pretty attached to Windows, then the point is moot.

*We used text-based browsers, PINE email, connected at 2800 baud to a free network at the University on a 50-megahertz 486, in the snow, uphill both ways...and we liked it!