it is more correct to compare with the height:
(Unit：CM)
2-3Y：Top length=37 Bust=61 pants=56, fits for: 90-100cm height / 2-3 Years Old

4Y：Top length=39 Bust=64 pants=60, fits for: 100-110cm height / 4 Years Old

5Y：Top length=41 Bust=67 pants=64, fits for: 110-120cm height / 5 Years Old

6Y：Top length=43 Bust=70 pants=68, fits for: 110-130cm height / 6 Years Old

7Y：Top length=45 Bust=73 pants=72, fits for: 130-135cm height / 7 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.