Personalized Dinosaur 3rd Birthday Youth T-Shirt. A dinosaur apatosaurus (or brontosaurus to the grandparents) stands tall over the 3 for the second birthday. Happy third birthday to the three 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.