I ordered one size bigger than what my daughter wears after I read the review.  But, it is still too small.

My daughter is size 8/10 swim suit but I ordered size 12 rashguard as all rashguards run small. This one fit perfectly, not snug at all and a little loose so it was very comfortable for her . The material is of great quality, not light and thin like other kids rashguards (Gap, Speedo, Target). I was pleasantly surprised and my daughter loved the pretty color and girly design.

Too small. Arm length is short. I have a child at the 20th percentile in size for her age (10) and still this was too small.