
My son is 68.2 pounds, 53 inches tall and wears size 10/12 shirts (but fits him better with a size 10 shirt on the side ). His 10/12 shirts are a little big for him, but not embarrassingly big. I bought this tropical shirt in medium size and it is too big. I could definitely buy a small one. The small size will fit any child wearing a size 8 or 10 shirt. The medium size fits like a large 12 or small 14 shirt. If he's wearing a short-sleeved t-shirt underneath like in the picture, he's fine. It'll still be big, but he'll be wearing it to a tropical school party, so nobody wears tight tropical clothes anyway.

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