My daughter is now 13 months, wears Clarks shoe size 4 and her foot is 12cm long. I ordered the 6-12 as well as the larger size, but the 6-12 socks
but they wouldn't stay on. After communication with Katie I decided to try the 0-6 instead and they fit great and stay on all day. My little one even picked them up excitedly one day and tried to put them on herself (we have the mustard yellow ones). I'll be ordering more in the smaller size.
Katie provides great customer service and sounds very polite and friendly.