Free planet-friendly building blocks

We all know that a refrigerator box makes a wonderful toy, but what about the small packages we throw daily into our recycling? 

I was at a friends house on a play date when she excitedly took out new cardboard "blocks".  "Forty dollars from Melissa and Doug", she told me.   They are terrific; the kids loved them – but I couldn't help noticing that they look and feel like the cardboard packaging for butter.  That gave me the idea to "make" my own.