Children are trapped in a set of rules they can't understand or control.
"Why do we have to move? All my friends are here." Well, because dad needs to switch jobs, because the company's downsizing, because profits are down, because the economy's fucked up, because the intricate invisible system that controls us all is shuddering and breaking.
Adults don't have much more knowledge or control, but we're tied into systems that we trust to understand things for us. We don't actually understand any of the crucial gadgets and systems that our lives depend on, but we can rely on the news, ads, other people to tell us that they're working fine. We can trust that everyone isn't lying to us.
Kids do not have this luxury.
So: Children don't understand the rules, can't control them, and they know everybody's lying to them about what the rules actually are. This creates a very specific and interesting mindset. Making a world that's a literal expression of an interesting mindset is a recipe for greatness. For instance, spy fiction has always presented a literal manifestation of a paranoid person's fantasies, a world where everyone really is out to get you.
In a million fairy tales, people are thrust into a world that works according to an intricate set of strange, often malevolent rules that are never clearly explained. This is the world kids live in every day, fishbowled around a child's perspective in the same way that spy fiction is fishbowled around paranoia. In the fairy tale, kids come to understand the rules, navigate them, and exploit them to their own ends. This is the heroic fantasy all children aspire to: attaining control and understanding over their lives.
Here's a classic example, Vasilisa the Beautiful. Vasilisa finds something that works in a strange way: Skulls that glow with inner light. Like the badass she is, she rips off a skull and uses it to light her way through the forest. She has come into contact with a creepy rule, understood it, and used it to achieve her goals.
In comparison, Scooby-doo is the purest wish-fulfillment. Not only do you come to fully understand the hidden and terrible forces behind the world, you kick them into the light to be humiliated and destroyed. It's like punching the GFC in the face. Even here, though, there's some melancholy. There are no vampires, werewolves or ghosts. There's never any real magic or forces of evil. In the end, it's always just a bunch of assholes trying to make a quick buck.