Pack of Hollow concentric Squares and circles in gradual sizes from 20cm down to approx 3cm 
Pack of 10 of each shape

They do nest if you nest every OTHER square, as in the main first photo. (So you can achieve two nesting sets with 5 squares in each set) 
Otherwise, you can stack each one as the borders are thick enough to stand each one on top without them falling through 

So many possibilities and fantastic for motor skills, balancing and using on a table to put small parts in
Chunky to hold, soft corners and robust in 18mm MDF