The show constantly refers to them as "storybook characters," hence the, ahem, clever name of the town. And "storybook" is generally used to refer to books with stories aimed at children. So that's hardly limited to Grimm's Fairy Tales.
That said, I really don't consider Frankenstein to be a story aimed at children. And if he is Frankenstein, that means a lot of screwed-up stuff should be around, too, least of which being his monster.