Personalized Mermaid 4th Birthday Women's V-Neck T-Shirt. Mermaid 4th birthday! A cute little mermaid celebrates your fourth birthday with her fish friends. Cute gift for the four year old. 5.0 oz., 100% pre-shrunk cotton Athletic Heather is 90/10 cotton/polyester 1x1 rib collar with mitered v-neck Shoulder-to-shoulder taping Ladies' fit