Here is the size chart for choosing the Watery Katsu Long-Sleeved Rashguard for Kids. This rashguard is sized based on your child's height and the length of the rashguard to help you find the right fit.
If you happen to be between two sizes, choose the one that's closest, depending on your preferred fit. If you want a snug fit, go for the smaller size; for a looser fit, choose the larger size.