Personalized Rawr I'm One Dinosaur Youth Long Sleeve T-Shirt. Rawr! I'm One! A cute T Rex dinosaur holding a megaphone and wearing a birthday party hat roars to let everyone know its birthday is here. Cute gift for your one year old's 1st birthday. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)