This is my first attack so be gentle
Take a sleeper of the same size you want your sleep sack to be and draw an outline around it to get the right size and shape. Sketch out the straps for your snaps (or buttons) as well. Mine are about 3" long.
Cut out one back and one front piece out of the lining fabric and the outer fabric.
Place the back pieces and the front pieces good sides together and stitch where I've marked in the pictures, from 'x' to 'x'.
Turn right side out and press.
Place the front and back pieces together and flip up the outer fabric.
Sew up the sides of the lining fabric starting where the outer and lining fabric meet.
Sew all the way up the side and around the corner, stopping a couple of inches in at the bottom, leaving a hole for turning.
Do the other side of the lining and sew the sides of the outer fabric in the same manner, remembering to leave the hole for turning.
Now you will have this:
Reach in through the outer fabric and pull the lining fabric out. This is when I check my stitches to make sure there are no holes.
Stuff the lining back into the sleep sack. Now you will sew up the bottom.
Sew the hole closed at the bottom of the sleep sack, trim the access.
Turn the sleep sack inside-out and sew along the bottom encasing the outer stitches in the seam.
Turn right-side out and mark the position for your snaps (or buttons). I use polyacetal snaps so that's all I have to show you. Add your snaps and you're done!
Phew! I thnk it took me longer to make the attack than it did to make the sleep sack! Hope you enjoy