I read Treasure Island over the weekend, too, and it's worth mentioning as a thought exercise in terms of the Adults Problem.
Set aside, for the moment, the various deus ex machina issues, which may have been less problematic for Stevenson's audience than for us. The boy Jim Hawkins travels with a variety of adult allies. How does Stevenson make sure that Jim is facing and overcoming problems?
The answer is that he repeatedly isolates Jim from his allies. Jim hides alone in the apple barrel to overhear the pirates. He leaves the camp alone and finds Ben Gunn. He frees the Hispaniola, again, all alone, and all alone he defeats the murderous Israel Hands.
P.P.S. Incidentally, here's a charming quote from Stevenson's "Appendix" to the 1894 edition:
"Sooner or later, somehow, anyhow, I was bound to write a novel. It seems vain to ask why. Men are born with various manias: from my earliest childhood it was mine to make a plaything of imaginary series of events; and as soon as I was able to write, I became a good friend to the paper-makers."
P.P.P.S. Turns out, Treasure Island was written as a serial, too.