Set of The Under Short (red) and Classic Shirt (blue) from Primary, both size 4-5. Shirt is 100% cotton and shorts are 93% cotton, 7% Spandex. From Primary website: A building block of a kid's closet, in bright solid colors you can't find anywhere else. Says customer Christy: "My kids love them and I love that they look brand new three years later and countless trips through the wash." Fabric: pre-washed to minimize shrinkage Feel: Incredibly soft and breathable.