Marina? Back theme to Stingray....

What sort of genre are you after? There are plenty of shanties that could be sung by children - I remember singing 'What shall we do with the Drunken Sailor' and others when a child. One of them was about a mermaid, and can I remember it now? No. I will know it when I see it, but it's just popped out of my head.

There's always the Disney stuff - 'Under the sea' from Little Mermaid springs to mind.

LTS