Our chalk looks different and so does the one (big and very soft) we call "stoep krijt" not only great to make drawings on the streets and walls but also to paint.

The minatures fit great in the "letterbak" (letter tray) or the tray they used to mold brick stones. I had one it was very popular in the 80s (attached to the wall filled with tiny sculptures - pretty expensive).

We made a mold out of gauze and wrapped gauze around this. A great technique but gios bandages are expensive by now and gauze alone is also quite expensive.
Paper maché remains 😁 It takes a long time to dry.
For years mujn children and I used it for Sinterklaas surprises - statues of cartoon characters. Later it became self-drying clay.

Plaster or concrete casting is also an option if you can make a mold or if you can work quickly and have patience you can build a statue with thicker plaster/concrete.

@grebmot @newton666 did you try something like this?