Amazing! The woombie that is sold on amazon at the moment is size 0-3 months (newborn and up to 13 lbs). There are many other sizes available at the woombie website. My baby was born 8 lbs 2 oz and was 10 lbs at 4 weeks. We started to use it since when she was 5 days old. Now she is 2 months and she still loves the woombie. She sleeps from 10 pm until 5 or 6 am! I couldn't find it the other day and had to use Kiddopotamus SwaddleMe blanket I had and she wasn't too happy about it. She doesn't like that the Kiddopotamus blanket is too tight and restricting. In woombie she can stretch and move around her arms and legs more.