Tell them they should scout their shoplifting locations beforehand to know where security cameras are to avoid being caught.
Just kidding, stealing's bad, here's an actual answer:
So, you'd probably want to ask them why they stole first. If they did it to fit in, if they were too ashamed to ask for money, if they wanted it but knew it was too expensive, etc. Deal with that first and cover the basis of that (doing dangerous things just to fit in isn't good and you shouldn't succumb to peer pressure, there's nothing wrong with asking for things from a parent, they should consult you and figure out how they can earn enough to buy the bracelet, you get the idea).
They're probably young (unless they failed a grade like, twenty times or something) so then you might want to explain to them why it's wrong. It harms the employees and could get them fired, if it's a local business, they don't make as much as big corporations do and stealing an item could seriously harm them. Establish some basic morals and let them know that their spur-of-the-moment action could have serious consequences for other people that did nothing wrong.
Then you can tell them that it's a crime and that it's illegal, and that they could go to jail for [x] amount of years, and actually, they're pretty lucky that the shop owner forgave them, and make them swear that they won't do that again.
TL;DR Ask them why they did it, explain why their reasons were wrong, get them to realize that shoplifting is a crime that can affect other people who didn't do anything wrong (the employees/the store owners), and that it could lead to some serious bad repercussions if they attempt it again, get them to promise not to steal again.
