I would say the shoe size for 18 mths. now is approximately 6-6 1/2. So I would buy sz. 7-7 1/2 in crocs. My daughter wore them last yr. when she was 1. (not walking yet) Her sz. was 4 & I bought sz. 5 crocs. She is 19 mths. now & in sz. 6 1/2 so I will buy her 8's for summer.--Did I confuse you? lol