These sizes are for guidance only, but if in doubt, we'd suggest going for the larger size as all these hats come with adjustable chin and head toggles to create a good fit and it'll last you longer, win:win!
Extra Small
43cm head circumference
Babies up to eight months
Small
52cm head circumference
Eight month old babies to two years
Medium
54cm head circumference
Two years to a bit bigger
Large
56cm head circumference
Little kids
Extra Large
58cm head circumference
Bigger kids (we'd suggest up to 8 years but please do check and measure as all children are different.)