Our sizes are professionally graded for optimal fit. It is common is to use age as the size, but it is important to measure your child as it is possible to have an older child that still needs a smaller size, or a younger child that needs to size up.
For example, a baby that is 14 months may still be wearing size 6-12 M given her measurements. Using weight and height is more accurate. If when measuring your child falls into two different sizes between weight and length (i.e. 17 lbs and 28'') then it is best to size up to ensure a better fit.
Garments in sizes up to 2 Y accommodate extra room for a (cloth) diaper. Measurements up to 2 years below are represented with a diaper on. The size chart below will give you guidelines for choosing the right size.