Personalized Unicorn 4th Birthday Youth Long Sleeve T-Shirt. Unicorn 4th Birthday - A pastel unicorn jumps over a colorful rainbow and smiling cloud. Cute gift for the four year old's fourth birthday! youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)