These cute pink clogs are brand new. Birkenstock's website indicates a kids size 30 is a kids U.S. size 12 - 12.5. They are convertible by adjusting a strap up to the top, or to behind the ankle. Photos show both ways. 

Classic style, designed with kids in mind. The Kay clog gives them a convertible backstrap that swivels up or down for added security when they need it. In durable Birko-Flor® that's smooth for them and easy to clean for you. This clog comes with all the comfort of the original contoured footbed.