"Just as other people have reported, this outfit is sized oddly. I have a petite 5yr old who currently wears 4T. I purchased the medium since I was worried about the width of the outfit. Sure enough the width of the medium outfit was fine (I doubt the small would have been wide enough) but unfortunately the length was way too long. I had to get out the scissors, needle, thread, and sewing machine. I will say that my daughter is very excited with the outfit. It just took a lot to get it to fit and was a bit pricey. The fabric probably isn't going to last for more that a couple of days but it will work for a halloween outfit and really does look like a mermaid. The foam tail was also starting to seperate so I stitched that around the edges as well."