Go to this site:
http://www.instructables.com/id/Rys-...-Turtle-Quilt/
A lovely lady has written some very complete instructions as she, too, feels that Simplicity...being mainly a garment pattern maker, has fallen down on the job of adequate instructions.
From me...WASH your fabrics before cutting!
Realize that you can make this more or less heavy by skipping the batting and just using multiple layers of flannel to achieve the weight you desire but remember WASH first, cut second. Good luck...I think that her instructions are good, just scroll down to find the "next" button below a couple ads...orange in color if I remember correctly to get to the next page.