Oilily sizing is slighty different to UK standard sizing if you are not familiar with the brand, you should email your seller to check the measurements

Size           UK sizing    Oilily sizing

3 - 6 m         68cm        62cm

6 - 9m          74cm         68cm

9 - 12m        80cm         74cm

12 - 18m      86cm          80cm

18 - 24m      92cm          86cm

2 years         98cm          92cm