Work on specially purchased finger paint paper or use regular paper made slippery with dish washing liquid. If paper is too flimsy use a counter, table top or student's tray and take a print of the finished masterpiece by pressing a sheet of paper over the creation. Short handled paint brushes are easier to control and regular house type brushes or paint rollers cover big surfaces quickly. Other things to try include sponge painting, vegetable prints, hand, foot and finger prints, stencils and spatter paint. S.E., Minneapolis, MN 55414-1312 and other sources.
Many excellent recipes are available.
Adult size are sometimes easier than small ones. 4A2 among other suppliers. My best find for 1995, battery operated electric scissors, very reasonable, and suitable for cutting paper and thin card from Radio Shack. Set on a table or wheelchair tray they provide a stable surface and prevent objects placed on the mat from being knocked off accidentally. 4A2 among others.