If your kids are motivated enough, they will find a way around it.
Reminds me of my local public library in 1997. They had these public computers for people that didn't yet have Internet access, and the browsers were locked down and stripped with just "back", "forward", "refresh" buttons and a URL address bar.
However, there was a tiny question mark icon in the corner that when clicked, brought up the Windows help system (that browser thing that can navigate help topics). There was a link in there to open IE and go to a support page, and when clicked would launch the full Internet Explorer with a complete menu over top of the kiosk interface, and this browser instance was not restricted in what it could access like the kiosk browser was (I believe it may have been a custom version of Mosaic).