This swimsuit is amazing! we love it. I can't remember if I upsized or not, but it fits well and has room to grow. I think I upsized one size just to be safe.
I ordered 3XL for my 7Y girl and it fits well. She is tall so usually wears 8Y. The quality is not like brand products but still not bad. It is hard to get this kind of styles so it is good.