Personalized 4th Birthday Mermaid 4 Year Old Toddler T-Shirt. This cute mermaid themed number 4 is just right for a little girl celebrating her 4th birthday party. A toddler-soft cotton tee in look-at-me, big kid colors. 4.5 oz., 100% combed ringspun cotton. White is sewn with 100% cotton thread. Topstitched rib crew neck. Double-needle stitched sleeves and bottom hem. Shoulder-to-shoulder taping.