Yes! I think it is called fusable webbing? I bought some recently. I ordered ds a dino t-shirt from ebay but when I received it, it was a mens XL (not sure how I missed that!). So, I cut out the pic, attached it to a child sized tshirt. I'm not sure how permanent it is, so I sewed around the edges, too. http://www.stitchemup.com/cornucopia/fusible_web.htm
I've seen Heat n Bond and Stitch Witchery in Walmart/ craft stores.