Crazy sizing

So I ordered these in a small for my 6 yr old for next winter. The first pants I received were the wrong size (a medium in a small pkg). I thought they could probably fit me. Sierra Trading Post was great about getting me out a small as quick as possible. The problem is I thought the small was actually going to be smaller than the medium and it didn't seem like it. Even with a year to grow, there is no way she would fit in them. These are going back to.