it is more correct to compare with the height:
(Unit：CM)
Size 3=5T-6T：Tops length=38 bust=86 shoulder=46 sleeve=14 Pants length=80 waist=51 hips=84, fits for: 115-125cm height / 5-6 Years Old

Size 4=7T-8T：Tops length=40 bust=90 shoulder=48 sleeve=15 Pants length=85 waist=54 hips=89, fits for: 125-135cm height / 7-8 Years Old

Size 5=9T-10T：Tops length=42 bust=94 shoulder=51 sleeve=16 Pants length=89 waist=57 hips=94, fits for: 135-145cm height / 9-10 Years Old

Size 6=11T-12T：Tops length=44 bust=98 shoulder=53 sleeve=17 Pants length=94 waist=60 hips=99, fits for: 145-155cm height / 11-12 Years Old

Size 7=13T-14T：Tops length=46 bust=102 shoulder=56 sleeve=18 Pants length=98 waist=63 hips=103, fits for: 155-160cm height / 13-14 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.