Personalized Mermaid 5th Birthday Youth T-Shirt. Mermaid 5th birthday! A cute little mermaid celebrates your fifth birthday with her fish friends. Cute gift for the five year old. 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.