US: 4-6 to Europe Size 21-23
Cross-market children’s socks, tights, hosiery, leg warmers, and dance tights sizing conversion mapping 4-6 specifications into 21-23.

Analyzing Size Equivalence Across Markets
US: 4-6: Corresponds to a foot length of 17.5 (6.9 ), matching US shoe size 10-12, and age range 48–84 months.
Europe Size 21-23: Corresponds to a foot length of 13.5 (5.3 ), matching US shoe size 5-7, and age range 12–24 months.