Japanese toddler size to printful size conversion?

Hey people,
I want to gift a custom t-shirt to a friend’s son (toddler, 4 and a half YO). I know his shirt size is 120 but I have no idea how it compares to the sizes on printful, which go by 2T, 3T, etc.

Does anyone happen to know? I can’t really ask to measure the size since it’s a surprise present