HELP - Shop Online Questions / How can I know which size is the correct one?

You don't know what size is the correct one?

Here is an age guideline that can help you:

Clothes

TU   55-62 cm      
0M   50-55 cm         3M   55-62 cm          6M   62-68 cm
12M 68-76 cm       18M   76-85 cm           2A   85-92 cm
4A   92-106 cm        6A   106-118 cm       8A   118-130 cm
10A 130-140 cm    12A   140-152 cm      14A   152-162 cm

Footwear 

15    9 cm               17    10,3 cm          18    11 cm
20    12,3 cm          21    13 cm             22    13,6 cm
23    14,3 cm          24    15 cm             25    15,6 cm
26    16,3 cm          27    17 cm             28    17,6 cm
29    18,3 cm          30    19 cm             31    19,6 cm
32    20,3 cm          33    21 cm             34     21,6 cm
35    22,3 cm