A recent discovery is the wonderful world if Makedo, based in Australia
Makedo is a connector system that enables materials including cardboard, plastic and fabric to easily join together to form new objects or structures.
When you’re done playing, simply pull it apart to reuse over and over again.
See their web site for inspiration. Fabulous ‘makes’ from the most basic materials – mostly cardboard boxes
Definitely right at the top of my ‘Oh my I wish I had thought of that’ list. I will be sending off for some of their connecting kits soon so I can incorporate this into my work.
http://mymakedo.com/what-is-makedo/
The Art of Play 
Here I am again Jane. I had more or less just finished doing a session with my small ‘brain boxes’ when I found this. Of course this is now top of my wish list for this re-constituted mind/brain/child/woman.