Personalized 3rd Birthday Mermaid Party Adult Sweatshirt. 3rd birthday party Adult Sweatshirt - White with blue mermaid tail for a little girl turning 3 years old. Stay warm and stylish with this classic adult sweatshirt, perfect for everyday comfort. Crafted from soft, durable fabric, it features a relaxed fit for added coziness. Whether you’re lounging at home, running errands, or enjoying outdoor activities, this versatile sweatshirt is a wardrobe essential for any season.