Children's Blocks

These blocks were interdependent and came in three colors: red, blue and yellow. They are entirely of plastic and are about the size of a rubix cube. Each block has a letter from the alphabet outside the block and each block open to reveal a figure of some sort. The figures correspond to the letter of the alphabet outside the block. We believe that the blocks may have been made by Mattel or others (some have even suggested that they were made from Tupperware). In both cases, if someone could please provide an answer, I'd be very happy.

They were made by Tupperware. They were called Busy Blocks. I found some on Ebay:
http://cgi.ebay.com/TUPPERWARE-BUSY-BLOC ...