I just did my third baby quilt with white fabric squares decorated by friends and family. I ironed freezer paper to the back of the squares, and gave everyone various fabric markers, pastel fabric crayons, etc. For the first two quilts, I drew what I intended to be the seam line on the fabric with a fine line pencil, with clear instructions not to go beyond the line. Well, some people appliqued and some embroidered, and while they were beautiful blocks, the stitching pulled in the lines - which didn't come out. For my third one, I drew the square on the back of the freezer paper with a heavy black marker, and this worked pretty well for the most part. Next time (if there is one!) I will do this again, but make it a little smaller than what I want the finished square to be, because I had to up the size a bit to accommodate some overenthusiastic artists!