Bought this for my daughter. She was 7 months at Halloween and this costume was enormous on her. Mind you she is a little small for her age but this costume didn't even come close to being a good fit. The sizing on this should be 9-12 months not 1 to 9 months. You could probably even get away with 6-9 months on the sizing but I have a feeling it would still be pretty large on an average size 6 month old.

Also, the antenna were really droopy and we had to hold out the wings to even show that she was a butterfly. She looked cute but she looked more like a pink lobster than a butterfly. :)