My daughter's foot is 6 1/2 inches or 17 cm and she wears size 10 street shoes. Based on reviews I ordered her slippers 1 size up and received her size 11C and they fit perfectly! She has a narrow foot, but the "C" fits her perfectly and she still has room to grow. Very well made shoes and they should keep them.
Breathable Fashion Sneakers for Baby & Toddler Boys & Girls: Bless Children Walking & Running Shoes
54 Review
Diadora Cattura Soccer Cleats Toddler Girls' Shoes for Athletic
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LEOCI Soccer Shoe Coomfortable Numeric_11_Point_5 Girls' Shoes and Athletic
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KUBUA Sneakers Lightweight Breathable Athletic Girls' Shoes for Athletic
53 Review
Capezio Girls 3800 Mary Jane Tap Shoe in Caramel - Size 11.5 M Toddlers
49 Review
Slip-Resistant Crib Shoes for Babies: Robeez Soft Soles for Girls and Unisex Toddlers, Ages 0-24 Months
53 Review
DREAM PAIRS Little Aurora 03 Communion Shoes and Flats for Girls - Top Choice for Stunning Style and Comfort
49 Review
Flexible Comfort: pediped Flex Isabella Mary Jane for Toddlers and Little Kids
47 Review