We bought a small for our 3 year old daughter and I had to hem up the costume by 4 inches at the bottom.  She is tall for her age and wearing a 4T to 5T, so I thought the small would fit her.  It does, but is incredibly long.  The sleeves at the shoulder are very  tight as well.

The hat has a tendency to not point up as it is made out of the fine mesh/lace that the sleeves are made out of.  The main part of the dress is a velvet-like material with an orange polyester/satin inlay with the lace/mesh over the top of the inlay.  The sleeves are the same polyester/satin with the lace/mesh over the top of that and hangs down a long way.  To keep the hat on, I HIGHLY suggest getting some matching ribbon and sewing it to the edges to tie under your child's chin.  That was the only way we could keep it on my daughter's head.

Overall, it is a very nice costume, but the sizes are on the larger end.  It looks like the Small fits more a 5T to 6T child, so be aware of that when ordering.  The small fit my 5 year old perfectly, and she is wearing 6T to 7T right now.