This is something I made while I was still pregnant (and before I started blogging so unfortunately I don't have any other pictures of them). But I'll explain how I did it.
1. Fold card stock in half
2. Use a onesie cookie cutter as a stencil. Make sure part of it is over the folded part of the card stock or else you won't have a card.
3. Stamp "thank you" on the front using a rubber stamp and white ink.
4.Tie a teeny-tiny bow out of thin ribbon and glue wherever you think looks best on the onesie.