Threadrock Big Girls' Big Sister of Twins Youth Long Sleeve T-Shirt Threadrock exclusive Runs slightly small; for a roomier fit, consider going a size up. Sizing: XS (2/4), S (6/8), M (10/12), L (14/16), XL (18/20) 100% preshrunk cotton; seamless rib knit collar; reinforced neck and shoulder seams; rib knit sleeve cuffs