Basically, every single childhood fable could be renamed to "Shut The Fuck Up" without losing too much in the translation.
Three Little Pigs? Shut the fuck up about knocking houses down and just do it.
Princess and the Pea? Shut the fuck up about your accommodations.
Boy Who Cried Wolf? Shut the fuck up.
Little Red Riding Hood? Well, you got me there.
For the most part, though, basically every classic story we tell kids has a lot to do with not making so much noise all the time. And there's a reason for that. Back in the 8th century, pseudo-nomadic Bavarian settlers began to suspect that their little part of Europe was not as unoccupied as they first thought. Something was there with them, and what's worse, it seemed to prey on the loudest members of their community.
Politicians, obviously, were the first to go, ripped apart and devoured in the middle of the night. Loudmouths of all stripes would eventually be consumed, they realized. Suddenly, a lot of street-corner hawking of goods and foods became extremely quiet. This period of relative calm caused a bunch of writers to have one fewer reason for procrastination, and many of them ended up "getting over their writers' block" for fear that their editor would yell at them and get the both of them masticated by an unknown, hostile force in the night.
Many children's stories were written, so many that the market became flooded from these productions. Customers would go to the bookstore, see a sea of Bavarian books, and become overwhelmed. Some would stick around, looking for a different region, but would leave empty-handed.
They had to do something, and that "something" was to invent the small mountain nation of Switzerland, which didn't actually exist back then, but has since developed a plausible backstory for its existence by a concerted government project to edit Wikipedia. Now, with the illusion of choice, customers could pick either a Bavarian or Swiss book. This problem was eventually solved on its own, once the authors became rich enough to move away from a country where they routinely ran the risk of being eaten by loudmouth-seeking monsters.
As a result, this tradition has carried on to the present day, often without childrens' fiction writers realizing that they were propagating this particular trauma for all eternity by imitating the works of their literati heroes.
Now you know the reason why children's books are all about being quiet. Or it could be that kids make a lot of noise. Both of these sound plausible, but just to be on the safe side, I would try not to shout while visiting any part of Bavaria.