Run large.
I bought these for my 8-year-old daughter. When we buy her new shoes, she gets blisters on the back of her heel.  They truly prevented the pain and blisters.  However, my daughter is a size 2 in girls.  They were so large that when she pulled them on, they came up over her heel and onto her leg by accident.  I wish they were a bit smaller.  However, they did the trick of keeping her blister free!
Rating: 4 stars