This is a kids toy that is made up of multiple extruded Octahedron shapes.

In geometry, an octahedron is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. From Wikipedia.

A unique property of octahedron's is that if you extrude the it along the x and y axis you create a shape that is stackable to create a larger octahedron. They can also be rotated will stack neatly.

The end result is a rather simple creative toy.

The shapes are based around 25mm Octahedron. To help prevent the risk of choking the smallest size comes in two forms, one is a solid, the other is hollow. The hollow cube will need support.

There are two sets of models, 0.5m, tolerance works well for me. But I included both in case your printer has different tolerance. The models were generated in OpenSCAD.

Link to documentation https://docs.ostat.com/docs/openscad/toy-stack-octahedron