Personalized Race Car 6th Birthday Youth T-Shirt. Race car 6th birthday Youth T-Shirt - Heather with red race car, checkered flags and big number 6. Side of car says BIRTHDAY CHAMP. Let the good times roll in a durable T-Shirt that takes kids from school to play in an amazing array of colors. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar.