Personalized Dinosaur 1st Birthday Youth Long Sleeve T-Shirt. A dinosaur apatosaurus (or brontosaurus to the grandparents) stands tall over the 1 for the first birthday. Happy birthday to the one year old! youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)