Isabelle: We could get into trouble.
Hugo Cabret: That's how you know it's an adventure.
Isabelle: This might be an adventure, and I've never had one before - outside of books, at least.
Hugo Cabret: I'd imagine the whole world was one big machine. Machines never come with any extra parts, you know. They always come with the exact amount they need. So I figured, if the entire world was one big machine, I couldn't be an extra part. I had to be here for some reason.
Hugo Cabret: I'm sorry, it's broken.
Georges Méliès: No it's not. It worked perfectly!
Georges Méliès: If you ever wonder where your dreams come from, look around: this is where they're made.
Lisette: Don't forget to smile.
Station Inspector: Which one? I've mastered three!
Mama Jeanne: Georges, you've tried to forget the past for so long, but it has caused you nothing but unhappiness. Maybe it's time you tried to remember.
Answer: He's not making it a point to chase down random children - he's like a security officer at an airport. It's his job to apprehend thieves and troublemakers and keep the station safe, and he only threatens to send children to the orphanage if they don't have parents for him to return them to. Also, it's implied once he finally apprehends Hugo that his particular harshness toward orphans (and most of his character flaws in general) is due to apparently having been one himself. He spells out the kinds of lessons he was forced to learn by growing up without a family, explaining how he became so cold, bitter, and antisocial.