I've made quite a few of them. I just serge the edge with a narrow rolled hem then just used my crochet hook to poke the hole through the flannel. Have never had a problem with it not going through. I just eyeball the distance and it turn out well. Fun to do and new moms just love them because they are so light. And the cost is so low - just takes a little time - but it's mindless TV work. Enjoy!