My daughter is transitioning to a size 5/6 these days and because I'm not sure how the sizes for different brands run, I decided to trust the sizing guide.  She had just been measured at the doctor's office (she just turned four), so I knew exactly what they were when looking at the chart and I was aiming to get it on the bigger size so it can last through the entire Wisconsin winter.  From the chart, I bought a 5/6 figuring that she should be almost drowning in the coat.  It arrived quickly and she LOVED it - it's very pretty and feels so nice....but when she tried it on, I had her put her arms straight out and turns out the sleeves were almost too short.  She is not disproportionate, so my husband and I decided to send it back for the next size up.  Now I'm waiting....and waiting...(can you tell I'm used to my prime 2-day shipping????) for the 6x.  I hope it's big enough to last through the winter because it really is a nice coat!