I bought this costume in size 12-18 months for my 17-month-old who is small for his age at 24lbs and the costume fit him great.  It is SO soft and SO warm!  It was very cold on Halloween but he wanted to stay outside and play because the costume kept him comfy.  Most Halloween costumes are made out of cheap and flimsy materials but this is a real heavy-duty costume here.  One thing I was a little disappointed in was that the tail hung too low that it dragged on the ground when he walked and we had to pin it up.