US Child/Youth sizing.
13US = 12.5UK = 31EU
1US = 13.5UK = 32EU
2US = 1.5UK = 33.5EU
3US = 2.5UK = 35EU
4US = 3.5UK = 36EU
5US = 4.5UK = 37.5EU
6US = 5.5UK = 38.5EU
7US = 6.5UK = 40EU