Personalized Butterfly Future Big Sis Youth Long Sleeve T-Shirt. Future big sister Youth Long Sleeve T-Shirt - White with smiling pink and blue butterfly with polka dotted wings surrounded by pink flowers. She says I'M GOING TO BE A BIG SISTER. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)