I know that this does not answer your question, but please give this some thought.
Since it is for a baby and will be washed many, many times please consider using something like the Eleanor Burns method of appliqué. I use the same fabric, right side to right side and sew around it. Then slit it in the back and turn right side out. Now you have an enclosed appliqué piece that you can sew down and it won't unravel. You can also put a piece of batting on it before you sew it to make it puff a little, and then cut off the batting outside the seam line.
Just a thought over coffee.....