I once stole a lollipop from a little girl
Why would you steal candy from a child?
I wanted show her the world is a bad place.
While what you say very well may be true, it's not up to you to teach that to a random child.  Stealing in general is wrong and you should've left it to her parents to teach her about the world.
Maybe you're right.  It sounds like I was naive to think that this would have helped.
You probably meant well, but the fact remains that stealing is wrong, and it only causes distress to others.  If you want to help children understand the world, you can try to give them gentle warnings about being careful, but even then, it's best to leave that to their parents.