Seeking some clarification.

Okay, I had this dream last night.  I'm sure I've dreamt it before, but aside from that, it's really, really familiar, and I'm posting about it here in case anyone else recognises it.  If not, then it's entirely of my own creation, and I'm going to write it as a children's book.

( Anyone else recognise this? )

I'm loath to put any more in case I do end up writing it, as the rest of the dream was the plot I'd vaguely use.

Is that even remotely familiar to anyone else?  Not just familiar in the "oh, that's like Waterworld" sense, or whatever, but actually familiar for what it really is?  Because I'm sure I've read it somewhere or seen a cartoon of it or something.  Just trying to figure out if I have, or if I really did literally dream it up...