According to customer's feedback, these turtleneck shirts run a little small. So we suggest that: if your baby is 2-3 years old, please choose size XS. 4-5 years old girls choose size S; 6-7 years old girls choose size M; 8-9 years old girls choose size L; 10-11 years old girls choose size XL. About the size details, please see the products pictures on the left side.