I bought this to go under my daughters lyrical costume as a recommendation from her instructor since the costume was itchy. She just turned 9 and has a slim build. I ordered the size 8-10 (medium). She was within the size guidelines. Normally she wears a size 8 pants and I have to pull in the waistband to the smallest setting on jeans. Elastic waists in a 7/8 are usually a good fit...10's fall off so I thought I'd be ok. This body suit has a very short torso so the straps dug in to her shoulders. I'm going to order the large but unfortunately this is considered a non-returnable item so I'm out more money. The bodysuit it self seems fine, just very small. The straps while clear seem a bit shiny. I hope they will not be seen onstage!