EU	AU	Foot length （CM）	Inner length （CM）
29	10.5 Little Kid	17.2	18.7
30	11.5 Little Kid	17.8	19.3
31	12 Little Kid	18.5	20
32	13 Little Kid	19.2	20.7
33	13.5 Little Kid	19.8	21.3
34	1.5 Little Kid	20.5	22
35	2.5 Little Kid	21.2	22.7
36	3 Big Kid	21.8	23.3
37	4 Big Kid	22.5	24
38	4.5 Big Kid	23.2	24.7
39	5 Big Kid	23.8	25.3

Example:

If your foot lengt is 20.5 CM ,You can choose AU 1.5 Little Kid