I got so tired of the kids sneaking onto the internet when they are supposed to be doing other things, here's what I did.
On the Droid, I turned on wifi, navigated to my router setup address, and created a blocked services profile just for their IP address.
I saved a bookmark for that page. Bingo! I pull up the page, activate the service, and their internet is blocked.
Now if someone would make a widget to do out with a single button press...