I bought size 6 for my petite 5 year old daughter and they fit comfortably.  My 2.5 year old(wears 2t shirts), tall, boy wears one, too.  While it looks big, it is not ridiculously large.  i would say they run a bit small based on my kiddos. My daughter loves them soooo much! I bought long sleeved shirts to tack to the inside so that she can wear them now without freezing. But, I can easily separate them when warmer weather comes.  Amazing deal to make my sweet girl so happy.