Personalized Superhero 4th Birthday T-Shirt. This kid is Four! Celebrate your child's second b-day with this cute thumbs up 4th design. Happy Birthday 4-year-old! Everyone loves our Custom T-Shirts! 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.