I'm 6'ft and wear 11-12
my wife is 5'5 she is only a size 1-2
Kids
Harry is 6ft and wears 12
Danny is 6ft2 wears 11
Aiden is 5'10 wears 10
Rich is 6'2 wears 12
Joe is 5'11 wears 10 (age 15)so still growing
luc is 6'1 wears 12 ( age 13) so still growing
All of the others are little kids and haven't finished growing yet but my 8 year old daughter already has bigger feet than my wife (size 3-4).
Clearly it must be hereditary in some ways, but how I'm not sure as my wife's family all have average sized feet and she's just got these tiny little things and is not particularly short, and her kids have normal sized feet.