Personalized Mermaid 1st Birthday 1 Year Old T-Shirt. Cute babys first birthday T-Shirt - Black that says this mermaid is one Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.