it is more correct to compare with the height:
(Unit: CM)
M=1T-2T：length=37 bust=64 sleeve=32;fits for: 75-85cm height / 1-2 Years Old

L=3T：length=40 bust=66 sleeve=33;fits for: 85-95cm height / 3 Years Old

XL=4T：length=41 bust=68 sleeve=34;fits for: 95-105cm height / 4 Years Old

XXL=5T：length=45 bust=69 sleeve=37;fits for: 105-115cm height / 5 Years Old

XXXL=6T：length=47 bust=71 sleeve=39;fits for: 115-125cm height / 6 Years Old
Note:
1.There is 2-3% difference according to manual measurement.(1 inch = 2.54 cm)
2.All measurement in cm, please note 1cm=0.3937ch, 1 inch=2.540cm
3.Please check the figures carefully and order the right size, don't completely depend on the " age advice". It's just for reference.