My house is like a little kid wonderland. We have every game console that you can buy on the current market, more games than you could play in a whole weekend, and a computer in just about every room. My kids also get more toys than any sane parent would buy because toys are cool. Despite all the cool stuff around here to play with, my daughter is always busting into my office and asking for a box to play in.
I can only imagine that she would spend more time pulling her Zhu Zhu Pets around in a box than anything else if she had something like the Rolobox that puts wheels and a pull string on the box. Honestly, I would have played with something like this more than anything else when I was a kid too.
It appears that the stuff sticks to the cardboard box with simple pushpins. I would bet there is something on the inside of the box that will hold the parts on or they would fall off constantly. Your kids should be able to use this set up with boxes of all sizes. You can order the kit up right now for $14.