My advice on a ruffle on a baby quilt is --don't. I remember one that was a gift when one of my babies was a baby. It was non-functional as far as warmth and was flipping around in the way of baby care. The only way a ruffle on a baby quilt is good is for decorative purposes. My opinion.
If you are really wanting to do this though, I'd advise making it not too wide, double and probably on the bias so it will hold its shape in laundry and be more durable than a single layer of fabric. If you have a ruffler for your machine, that will be a big help creating the piece and it will hold its shape while being attached to the body of the quilt.