Earlier quoted context omitted.
These stories weren't meant to be children's stories. They just became popular as such and have been edited to make them more child friendly to the point that with Disney they're hardly recognizable anymore.
That's not remotely true. Many of these stories were specifically to protect children. If you can't watch your children all the time, you can't just tell them, "Don't go too close to the water." They'll go anyway. So you tell them, "There are Wassermen (German) / Vodnik (Czech) who will grab you by the feet and pull you in."
Others tell you that your family is evil and you should seek advice from talking animals instead.
But the original was published as "Kinder- und Hausmärchen" or "Children's and Household Tales," so you're right that the Grimm's fully expected these would be read to or by kids.