Airtight buckle design can be used for children 3-13 years old.Size of 4-5years S :Suitable for height 31.5(In)-39.5(In)��Suitable for weight 44 (Ib) 6-7years M :Suitable for height 43.5(In)-55 (In)��Suitable for weight 66 (Ib) 9-10years L :Suitable for height about 55 (In)��Suitable for weight 88 (Ib)Material: High-density non-toxic PVC plastic.