This would be more of a jersey knit swaddle blanket... not quite the muslin swaddle material!

Jersey swaddle blankets. You can find a lot on Etsy 

Muslim blankets, I got mine from babies r us, and I love them my daughter loved them, and they were so convenient during her summer months because they're thin and allow the blanket to breathe in a way.

Try Milkmaid Goods...awesome site with super cute swaddle blankets.

They are swaddle blankets. I don't think there are different names for it. Check on Amazon. They have a huge variety, and so many different sizes. I got a Muslim swaddle from there for free, and it is so soft and big, and I love it! I also got a 3 pack from Burlington, and although it's the same size and material, they aren't nearly as soft.

I think they are called Muslim blankets ?? Or muslin ? Something like that..... I think 

Muslin blanket ?

I ordered this one on Amazon for like 5 bucks. It came from China.. but it was the same thing I saw on Etsy for 1/4 the price. 

Loulouandcompany.comKbcutedesignsCozysAll great companies with these big soft jersey knit swaddles. They add new prints often 

I've also heard them being called receiving blankets.