They should be given small pans of water and large brushes. Some roll-on deodorant containers have a removable ball. Wash container and fill with paint. The children can then roll on the paint.
Evaporation leaves crystals.
The design is duplicated by covering the paper with another sheet and rolling it with a rolling pin. The edges of a spool are nicked for design. A wire is inserted through the spool and twisted to make a handle. The spool is then dipped into thick paint and rolled on the paper.