Since my Blue Crab piece will be traveling for a year in a Hoffman Challenge Trunk show, I made a small (no-sew) blue crab out of the fabric scraps to remind me of my larger piece.
The design is pre-cut into a form core with a sticky surface on top. You peel back the top layer of a piece and use that as the fabric pattern piece. You cut your fabric piece about 1/4″ bigger than the pattern piece and then place the fabric on the sticky form core and stuff the edges into the pre-cut slots in the form core with the back side of your seam-ripper.
These tuck and go pieces are fun and easy. They would be a great project for kids since there is no sewing required.
There are a number of companies that make these kits. Here are some sites: