A dab of Elmer's washable school glue around the edge will work depending on how you are going to finish the appliqués. Try a sample on a different background square and a spare appliqué. Use a toothpick to smooth a little glue around the appliqué edge and stick it to the background. Press with the iron and see how you like it. If you are going to satin stitch the edge, try that and see how it goes. If you are going to use a buttonhole stitch on the appliqué, I don't know if the glue will be enough to hold it.