I purchased this in size 4T for my 6 year old grandson, he's average size, just finishing up kindergarten and loves dinos. This was a great fit for him. He's growing like a weed and this has just enough give in it to get him through the last couple of months of school and through the summer. If it survives all of that, I think he'll still be able to wear it at the beginning of the next school year. I was surprised. It does say 5-6 years, but usually a 4T is too small for a child that age. I would not go by the size, I would go by the years listed. Very well made, good quality fabric and the design is great. The length is proportionate with the size, as is the neckline and sleeve cuffs. There are 4 designs ranging in size from 2T to what is listed as 6T. They correspond from age 2 years up to 6 years. Great shirt, kids are going to love the graphics.