You can find measurements on the page products.
Size up for the boxer , rashguard and one piece as they fit little bit small.
If your kid is 4 years old but dresses in a size 6 ---> size 7/8 Y
If your kid is 3 years old and dresses in a size 3 ---> size 3/4 Y
If you have a long torso we recommend to choose the Giulia Set instead.
Tips: The printed swimsuits ( Stripes & Geometric print) are little bit less stretch than the color block ones. if your are in between sizes better size up.