I got the stencils from Microsoft Clip Art. They're a little more detailed that this, but I opened them up in Illustrator and deleted all the extra paths and layers that weren't necessary, and brought them down to these simple designs.
The goat was probably the most difficult, being a three layer stencil, but it came out all right. I think it looked better on paper that it does on the onesie, but that maybe because it's being compared to the other four simple designs. The goat is actually a horoscope picture, and not even the baby's, but the kid's name is Billy. Get it? Billy, goat? Billy Goat?