this sock is SO tight. I ordered a medium for my kids who wear a youth size 3 shoe. they are 6 yrs old. This size should be plenty big, but it's so tight you can barely get their feet in them, plus they are super tight around the ankles and this can't be comfortable. My children are all average size on the growth charts, so I know it's not their issue, it's the socks.  I expect after they are washed (c'mon who washes socks in cold water as the maker instructs?) these will fit toddlers.  They are also NOT seamless.  The seams are smooth and tighter than say, Hanes, but still there.
Again, these look and feel really nice, but what's the point if they don't fit and you can't bleach em and wash em on hot?