Size Small: Suitable for children younger than 4, who weigh less than 40 lbs.
Size Medium: Suitable for children aged 5 to 6, who weigh between 40 and 55 lbs.
Size Large: Suitable for children older than 7, who weigh greater than 55 lbs.
If your child is in between sizes, such as a child who weighs around 40 lbs., or is 4 1/2 years old, order a smaller size if the child is taller/thinner than an average child of their age, or order a larger size if the child is shorter/heavier than an average child of their age.