What do you need?
a transparent printer sheet
glaspaint or Ecoline, in primary colours
a paintbrush
Give your mini-monters a transparent printer sheet, some Ecoline watercolours and a paintbrush and they will make a beautiful stained-glass effect painting, for Sinterklaas. Let them paint on the rough back of the printer sheet, Ecoline does not stick on the glossy front. Otherwise use glass paint, that sticks just fine.
How to make a stained glass painting
Look at Marijke's steamer! This work of art is of course for St. Nicolaas, who else could it be for?