The size is S. I think it can be worn until around 0-3 months! The ivory one is a beautiful item that I purchased here, having only been washed. I purchased the gray one from another site, and it has signs of use. I used the two interchangeably for about two and a half months, only at night. My child slept well when wearing a swaddle, so it was a great help! The gray one has some pilling and shows signs of use, but it's not torn, and it's convenient to have two, so I'm selling them as a set. There is pilling and fuzzing, but there are no stains. The hat is only tried on. I think neither is suitable for those who are sensitive or concerned about pilling. It's recommended for those who want to try them out or want to save money, as they are likely to be worn only at night for a short period.