This was so quick it barely counts as sewing.
I bought 30cms of Nani Iro double gauze. Folded it lengthwise (right sides together) & sewed up the sides leaving a gap to turn it the right way. Then I simply clipped the corners, turned it right way out & hand stitched up the hole. The whole process took about 10 minutes.
It's isn't big enough for me, but it is the perfect size for a child & being a double gauze it is lovely & soft.