I ordered this set of thermals for my 4 year old son. He’s pretty tall for his age, so I thought the XS which is a size 4,5 would be perfect. The set fits great. He can wear it now and it will fit for the entire winter over the next few months. I love to have thermals for my kids to wear under their snow clothes, and these are going to work great as that base layer. The rich black is a great color too.