Reference size:
XS: Back length 20CM, chest 32CM
S: Back length 25CM, chest 37CM
M: Back length 30CM, chest 42CM
L: Back length 35CM, chest 47CM
XL: back length 38CM, chest 52CM
XXL: back length 42CM, chest 57CM

XS (recommended weight 0.5-1.5kg)
S (recommended weight 1.5-2.5kg)
M (recommended weight 2.5-4kg)
L (recommended weight 4-5.5kg)
XL (recommended weight 5.5-7.5kg)
XXL (recommended weight 7.5-10kg)