Definitely one size bigger. I bought size 8 for my 6 year old. She is of average height and very thin. I bought one of these turtlenecks for a Halloween costume (green, perfect color for a dinosaur, dragon, crocodile). My daughter continued to wear it. After a year it became too small and she wanted to wear the same suit, so I bought another one, 2 sizes bigger. She continues to wear it as it is soft and comfortable. It's like a t-shirt material, not thick. So I bought this red just for a change. The color is excellent. True red, not pink. The turtleneck sweater keeps her warm on the way to school, but the material is so thin that she doesn't boil in the overheated school building.
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