When a mermaid is first born, they look something like a little baby, but instead of feet they have a tail. When they are a kid, They get to decide whether They become a mermaid or a siren. It depends on their behavior. If they are mean and cruel, they will become a siren. If they are kind and sweet, they will become a mermaid. But there are some sirens who have to be sirens, or mermaids who have to be mermaids. If a child is a siren but they are nice, there will be a heart on their cheek. If they are a mermaid but are mean, there will be a storm cloud and lightning bolt on their cheek.