Running Scared (2006)

Joey Gazelle, a low-level mafioso, is given the task of disposing a gun used to kill corrupt cops. Instead, he hides the gun in his basement. Oleg, a young boy, witnesses this. When Oleg's stepfather abuses him, the boy steals the gun and shoots him. Now, Joey must find Oleg and the gun before the police and his mob boss do. Along the way, Joey encounters various criminals, pimps, and a couple involved in child trafficking. Eventually, Joey reveals he is an undercover FBI agent and, with Oleg's help, takes down the mobsters and saves himself and the boy.