This is what you are reacting to in that song,” Minchin said. “You have a slight sadness when you are a grown-up. You’ve stopped climbing trees and you do not know when that happened. Maybe you’ve already climbed your last tree. You feel a loss of innocence, but you are also facing the truth that you are not the grown-up you thought you would be as a child. You’ve lost your childhood, but you’re actually still a child. And you never got your super powers.
Tim Minchin, on “When I Grow Up” from Matilda : One man’s obsession with one song from ‘Matilda