This is the one and only time I'll advocate for stepping on little fuzzy friends, because they're technically the one's doing the stepping! I may not be an ethics professor, but that seems pretty humane to me!

Size Youth fits children ages 5-8.
Size XS/S fits Womens' shoe US sizes 5-7. Mens' shoe US sizes 3.5-5.5.
Size M/L fits Womens' shoe US sizes 8-10. Mens' shoe US sizes 6.5-8.5.