Personalized 3rd Birthday Mermaid Party Youth T-Shirt. 3rd birthday party Youth T-Shirt - Pacific Blue with blue mermaid tail for a little girl turning 3 years 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.