EU	AU	Foot length （CM）
26	9.5 Little Kid	16.5
27	10.5 Little Kid	17.2
28	11.5 Little Kid	18
29	12 Little Kid	18.5
30	13 Little Kid	19
31	13.5 Little Kid	19.6
32	1 Little Kid	20.2
33	2 Little Kid	21
34	3.5 Big Kid	22
35	4 Big Kid	22.5

Example:

If your foot lengt is 18.5cm ,

You can choose AU 12 little kid