Personalized Superhero 4th Birthday Youth 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! Let the good times roll in a durable T-Shirt that takes kids from school to play in an amazing array of colors. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar.