23rd Oct: It's time for the Second TV Tropes Halloween Avatar Contest! Details here.
A kid and his parents are on a camping trip. Happens all the time in real life, nothing unusual here. But the kid decides to explore a little bit, and before he knows it, he's lost. Or a bear shows up and threatens the family, and the kid ends up separated from the parents. Or whatever happens... basically, the kid ends up separated from the adults. And ends up going on his own adventure, naturally. This happens all the time in kids' stories. It's one thing to have a Kid Hero who runs around the place, encounters criminals, and stops them singlehandedly, but that's not very convincing. And having a kid and the parents go on an adventure and get into danger at the same time often isn't as fun as having the kid go on solo adventures. By separating the kid(s) from the adult(s), you have a more convincing, "realistic" reason for the kid to be alone while getting into trouble or danger. As such, this is how lots of adventures start, or how they escalate.