Personalized Happy Pi Day Pink Math Symbol Toddler Long Sleeve T-Shirt. Cute pink pi math symbol with stitch border on a Toddler Long Sleeve Tee - Black with Happy Pi Day quote. A classic for Fall, Winter and Spring, these long sleeve toddler t-shirts are sure to be a staple in your child's wardrobe. Whether layered or alone, this t-shirt is soft yet durable enough to stand up to your toddler's playtime demands.