I suppose the main moral of this one is to not mistreat those that helped you in times of trouble, and the King pretty must says exactly that as he’s forcing his daughter to share her food with the frog. However, the story as a whole does not reflect that, in my opinion.
I mean, the princess was planning on deceiving the poor amphibian from the very start. And as she was forced by her father to accept the frog’s “I AM YOUR BFF NOW” deal, she despised him more and more, where she finally intends to kill the disguisting thing by throwing him hard against a wall. So when he suddenly turns into a beautiful rich prince instead of dying, she’s basically rewarded for murder.
Throughout the story I was under the impression that the princess was a small child, around 5-7 years old. I mean, I know people used to marry early in the “olden days”, but that still sounded wrong when by accepting the frog’s terms (I’ll be your companion now) she in fact agreed to marry him in Prince-Charming form.