Personalized Whatif Monster Birthday Girl Youth Long Sleeve T-Shirt. There's no day like your birthday, so why not try something new? Whatif Monster Birthday Girl Youth Long Sleeve T-Shirt - Red, perfect for little fans of "Jonathan James and the Whatif Monster" by Michelle Nelson-Schmidt. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)