This is a kid’s book (I read it in a about twenty minutes, so I wouldn’t even give it full YA status). And it’s surprisingly dark.
This is the story of the Frog Prince, while he’s a frog. He meets up with a lady frog in the pond near the house of the hag that turned him into a frog. The lady frog is completely confused by the newcomer – he doesn’t seem to know anything about being a frog.
He gradually figures things out, and he and the lady frog go on to have kids. Which turns out to be an interesting experience for her, as he actually wants to take care of them.
So after all that, where the frog family basically learns to be human, he gets turned back into his princely form when he thinks he’s saving one of his kids. And that’s that. It was actually surprisingly sad, which I wouldn’t expect to run into until at least a true YA level book.