I have found that ten and a half to twelve and a half inch blocks are a good size for kids to work on. Cut out a square for each student. This will stabilize the fabric so it is much easier to draw on. I usually encourage students to make a rough draft of their drawing on a sheet of paper and to draw their design in pencil on the fabric before beginning. I use a rotary cutter for all the above and an old blade for cutting the freezer paper.
Kids can draw directly on the fabric so what they see is what they get.
These are soft like oil pastels and blend beautifully. Encourage kids to use bold strokes. The blocks will need to be heat set following the directions that come with the crayons. The best place to find the crayons are arts and crafts stores. Instead of pressing the stamp into the sponge, dab the paint on the stamp with the sponge.