Detective Conan: The Time Bombed Skyscraper (1997)

Once brilliant teenage detective Shinichi Kudo was given a poison that reverted him to a 4-year-old. He's adopted the pseudonym Conan Edogawa so no one (save for an eccentric inventor) will know. Now he's got to solve a series of bombings before his loved ones become victims. Who is this madman and why is he doing this? Only the young genius can save the day but will even he be up to the task?