Personalized Mermaid Princess 6th Birthday Youth T-Shirt. 6th birthday Youth T-Shirt - Black with a beautiful little mermaid princess wearing a crown atop her red flowing hair and surrounded by cute fish and starfish. Text says THIS LITTLE PRINCESS IS 6. 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.