Personalized Happy Pi Day Robot Math Class Toddler T-Shirt. Pi Day Toddler T-Shirt - White has funny vintage style robot and math symbol Happy Pi Day celebration logo. A toddler-soft cotton tee in look-at-me, big kid colors. 4.5 oz., 100% combed ringspun cotton. White is sewn with 100% cotton thread. Topstitched rib crew neck. Double-needle stitched sleeves and bottom hem. Shoulder-to-shoulder taping.