My Captain, Mr. Underground (2006)

A notorious grave robber Dae-chul steals a precious Buddha statue. As fate would have it, two kids Ji-min and Byung-oh steal it from him for fun. Dae-chul tricks the kids telling them that he is a special agent from the Ministry of National Treasures, and persuades the kids to help him in the cause of justice. As they experience one mishap after another, the kids and Dae-chul form a family-like relationship.