Personalized Superhero 3rd Birthday Long Sleeve T-Shirt. Happy 3rd birthday! Celebrate your toddler's third b-day with this cute I'm 3 superhero design. Happy Birthday three-year-old! Pre-shrunk 100% cotton 6.1 ounce long sleeve t-shirt. Double-needle stitched neckline and sleeves. Quarter turned. Shoulder-to-shoulder taping. Adult: S, M, L, XL, 2XL, 3XL