Personalized 6th Birthday Monster Truck 6 Year Old Youth T-Shirt. Colorful boys Monster Truck 6th Birthday Youth T-Shirt - Pacific Blue for his big birthday party day. 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.