Kodomo Keisatsu (2012)

Red Venus, with Yokohama as it's base, is an organization that mediates various crimes... In order to arrest such an evil organization, a Special Investigations Division was set up at the Kanagawa Prefecture Police Department. The group of elite detectives are just about to be able to get to the bottom of everything, when they fall for a trap. They get trapped in a harbor warehouse, where they are intoxicated with the special gas that the Red Venus created, and as a result the members of the Special Investigations Division...turn into children!! Welcoming in an adult rookie detective, despite being in their child form, the Special Investigations Division continue on with their investigation to arrest the Red Venus. In the midst of all that, a murder case arises and the Red Venus is seen as reponsible for it. While attending school, they continue on with their investigations! When they finally hone down on the suspect and just as they are about to get to the suspect, the Red Venus beats them to it. Will the Special Investigations Division really be able to arrest the Red Venus!? The battle of the child-turned Special Investigations Division begins! --TBS