Origin of the Word 'Sandbox'

As I stood in front of my class that first night, I dug deep inside myself for the one thing that I stood for, the one thing that would charge up the class to leap into the media with gusto and pizzazz. Then I thought of the magic word: sandbox. To me a sandbox is more than four boards and a bag of sand. It is a metaphor for play, storytelling, world building, and for a child's personal journey of exploration and discovery. And sand is a metaphor for what good media should be?rich, malleable, and gritty. Playing with media should be a multisensory experience. As with sand, you should smell it, taste it, and touch it. It should get in your ears, in your shorts, and in your hair.

http://www.atarimagazines.com/compute/issue76/World.php

I want to quantitate the sandboxiness of something as 'milli D'Ignazios'

What do you think?