This is the size chart from Disney shopping website. First number is size.
2 XXS 31-34" 26-29 lbs 1-2 yrs
3 XXS 34-38" 29-33 lbs 2-3 yrs
4 XS 38-42" 33-37 lbs 3-4 yrs
5 S 42-45" 37-43 lbs 4-5 yrs
6 S 45-48" 43-50 lbs 5-6 yrs
7 M 48-51" 50-57 lbs 6-7 yrs
8 M 51-54" 57-67 lbs 7-8 yrs
http://img.dsi.go.com/content/global/guest_services/sizes.html#Kids
2 XXS 31-34" 26-29 lbs 1-2 yrs
3 XXS 34-38" 29-33 lbs 2-3 yrs
4 XS 38-42" 33-37 lbs 3-4 yrs
5 S 42-45" 37-43 lbs 4-5 yrs
6 S 45-48" 43-50 lbs 5-6 yrs
7 M 48-51" 50-57 lbs 6-7 yrs
8 M 51-54" 57-67 lbs 7-8 yrs
http://img.dsi.go.com/content/global/guest_services/sizes.html#Kids