"I initially ordered a size up in these shoes based on previous reviews stating they run small. That was a mistake. My 4 year old daughter wears a 9-9.5 and the XS (9-10) is actually a tiny bit big. Nothing an insole can't handle, but they were most certainly NOT too small. Perhaps there is some sizing difference in different lots, which would account for prior reviewers experiences. I ordered both a S (11-12) and an XS (9-10) and there was not a huge amount of difference in the size of the shoes, so maybe the larger sizes run small? Dunno, but my daughter LOVES these shoes - especially because they have a heel "just like Dorothy's.""