I dislike the sizing chart they give... I guessed with my daughter. She was wearing size 7/8 at the time and I ordered the intermediate size and it was great. Lasted the year and now we're moving up. :) Because they are mostly cotton, they did fade and roll up a little at the bottom, but it wasn't noticeable on stage.
Daughter is 26" 22" 28" and almost exactly 5' tall, and wearing these as a low-rise waist pant (as pictured) they were about 3" too short :( Hopefully adult xs will be skinny enough, as they look & feel great otherwise.