Thank you for the good ideas! I rolled the dice and tried a couple of things. I went ahead and purchased the tumbled tiles. One design, which was not totally colored in, I drew freehand with Sharpies. The other design, which was all colored in, I purchased an acrylic craft paint and used it. I sealed both with matte waterproof sealer. They really turned out quite well! Hopefully, they will sell and earn some money for the Children's Protection Network!
Thank you again, stampers!