A show that fits your description of teenagers being thieves in an espionage genre is "Cloak & Dagger." It's a Marvel series that follows two teenagers, Tandy Bowen and Tyrone Johnson, who develop mysterious powers and become embroiled in a larger conspiracy. While they aren't traditional thieves, they do engage in covert operations and have to navigate complex moral dilemmas.
Another example is "The Perfect Score," which revolves around a group of high school students who try to steal the answers to a standardized test. While it's not purely espionage, it involves elements of theft and planning.
If you're looking for a more classic example, "Leverage" includes a team of thieves and con artists, though the main characters are not teenagers.
If you have a specific show in mind, please provide more details!