What things in children's books didn't make sense to you at the time, and only became clear much later?
In The Railway Children, when the children prepare a birthday surprise for Perks, I didn't understand his appalled reaction at all, even when people tried to explain it. I thought that if he was indeed "poor", why would he be anything but grateful? I used to skip that scene when watching the film.
I was blissfully unaware of social class as a child: in Roald Dahl's Danny the Champion of the World, the significance of the obnoxious Mr Victor Hazell driving a Rolls-Royce went straight over my head. Near the end of the book there's a scene where his Rolls Royce is damaged by his own pheasants, and I remember not understanding that scene at all: I thought it was Dahl silliness thrown into one of his more serious stories.