Personalized 4th Birthday Mermaid Party Toddler Long Sleeve T-Shirt. Cute 4th birthday mermaid Toddler Long Sleeve Tee - White with a blue mermaid tail for a 4 year old party photo. A classic for Fall, Winter and Spring, these long sleeve toddler t-shirts are sure to be a staple in your child's wardrobe. Whether layered or alone, this t-shirt is soft yet durable enough to stand up to your toddler's playtime demands.