Kurt Naef's Building Blocks (1955) were among the first of his designs for children and a core component of his Basel-based company’s educational philosophy. These blocks can be stacked and nested to form staggered constructions—bridges and towers, for instance—stimulating a child’s creativity. Ages 3 and up.

Don't have a 3D printer? You can now order them directly from Shapeways ($103.27)! http://www.shapeways.com/model/736492/naef-building-blocks.html

(A set of 16 in wood is $160 at the MOMA Store: https://www.momastore.org/webapp/wcs/stores/servlet/ProductDisplay_Naef-Colored-Building-Blocks_10451_10001_141198_-1_26698_26700)

This thing was made with Tinkercad. Edit it online https://tinkercad.com/things/4GMNHdAasD5

Print as many as you'd like in all kinds of pretty colored plastics that you have! The more, the better. This scale is at 2" blocks, the original size, but you could probably make them smaller or larger if you'd prefer!