My daughter received this for her 5th birthday. She is of average height and is thin, we ordered her a medium and it fits perfectly. The coverage on the behind is great, as this is a modesty concern of mine.
This outfit has got everything, a great price, great fit, and great quality.
It does recommend hand washing (I don't hand wash...), but my daughter got green food coloring on it the first time she wore it and I put it in my top loader washer in a mesh bag on the low adjtation cycle and it washed up really well. I did not put it in the dryer.