My son is 5 years old and I ordered a size M based on previous reviews. It fit perfectly; I don't think he would have fit into a Small! I do think it's a bit pricey for just the vest and hat, but my son really wanted to be Toad this year. He's in love with everything Mario Bros. right now. I found the khaki colored shirt online at Walmart for $3.99 and I bought him long white baseball pants, which were on sale for $7.99. Can't beat that!