Personalized 6th Birthday Boy Rocket Youth T-Shirt. 6th Birthday Boys Rocket Ship Youth T-Shirt - White in striped blue and white with number 6 on this space themed bday gift. 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.