My babies have both been tall, and they are quickly too long to swaddle in the little receiving blankets, so I use these square flannel blankies instead. At 2 1/2 weeks, Raven is already needing the larger size, and we've somehow lost nearly all the ones I made when Monkey was born so I'm making a few new ones. These are simple double flannel squares, and they're a great size that works for swaddling now and dragging around when the baby gets older. I do squares because I prefer to swaddle in a square, rather than a rectangle.
2.5 yards of flannel
The idea is to have a piece of fabric that is twice as long as it is wide.
Fold your fabric in half right sides together.
For the most part, I use a standard 5/8ths seam. However, flannel often has a "don't use this for children's sleepwear" warning, and on that side I use a larger seam to make sure that the warning is completely hidden on the final blanket.
Start sewing about 8 inches from the fold. Go all the way around the open edges of the fabric, until you come back to the fold.
Clip a triange off the corners to reduce the bulk of fabric there when it's finished. Turn your blanket right-side out through the opening you left in the seam. Make sure your corners are fully turned as you go. Iron the blanket flat. When you iron, make sure to iron the open spot with the edges to the inside of the blanket, so that it looks closed as it sits there. Then, when you go back to your machine, start with the open spot.
Topstitch all the way around the blanket, which should close the opening you left. I like to make this seam as wide as my machine's foot.
That's it, you're done! Swaddle your baby in your new blanky!