I'm currently in Victorian London having to exist while random people with knives on their wrists keep killing leaders of major corporations and politicians.
Assasin's Creed, eh? Sounds like you're fine as long as you're not a major politician or leader of a corporation. Maybe you should hire those knife-arm people as bodyguards.
Then go get it back. It's Victorian London, right? Call the cops. Fun Fact: Victorian cops were called "Peelers" after the person who invented the police force, Sir Robert Peel.
Then take matters into your own hands. Don't hurt the kid - he probably has to work in a factory and stole your stuff to sell it since his pay is pitiful - just strongarm him. If you're not up for that, try the cops again. Most Victorian police officers are former criminals.
Yes. However, murder is still technically illegal, as is theft. You do both in the assassin's Creed games. In syndicate, you can hire kids to steal stuff for you.
Okay. Well, morally speaking, you could probably appeal to the assassin and get a new shirt, or get your old shirt back. When push comes to shove, you can try paying him.