My 6yr old is a size 22 chest & a size 5 fits perfect!
I also have a size 6 & it too is a good fit but 5 fits better.
I washed & dried these on the hottest settings to see if they would shrink & they do not! ALSO you do not need to iron them either, straight from the dryer to the hanger! These also come down right below her knees.
Very well made! I will be buying more!