I once did something based on the same principle, for a (very-very light) security solution, atop a simple closed-source media appliance that could play from USB Storage. I made a script on Linux to create a huge directory tree representing every possible sequence of a password of length N. Only one password path through the tree got the viewer to the directory that had the non-kid-safe media files. The non-security…
Love this, but seems to me that if most directories didn't have files, you could `find` your way through...
If you had only the dumb appliance UI, however, finding the files would be a bigger chore than even energetic kids could accomplish in mere hours, and only if they knew it was there (the "password UI" was also hidden a little).