One size smaller! Bought 7/8 and 10/12 for my 3 boys. My skinny 10 year old needs 7/8 which I bought for my 7 year old lol. And my chunky tall 8 year old who normally wears 10/12 had to roll up his sleeves and he was baggy. BUT it held up well in the wash and didn't shrink too much. And they look great so they take some time to get used to as they have space.
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