Personalized Monster 4th Birthday Youth T-Shirt. Cute 4th birthday Youth T-Shirt - Kelly Green with a funny cartoon purple monster, stars and polka dotted number 4 says THIS LIL' MONSTER IS FOUR! 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.