Hi there,
I can write this in a week, a perfect children book on this niche. I'm already getting ideas. We can create 4 characters, all of them can be sisters, a blue, green, pink and yellow mermaid. The pink mermaid's going to be the main character, who's the eldest of all and is to be wedded soon, but a suitable match is yet to be found. They'll have a father who's the king of Atlantis (the ocean world) and announces that whoever brings this "Golden Pearl", that is protected by the dangerous water dragon, will be chosen as the right partner. This is what I could come up with right now, I'm sure I can make it much better when I do it properly. I'm an illustrator too, I'm a complete artist and would love to draw for this book if you want me to. Let's get in touch please.
Cheers! :D
Words Alchemy