Naani an eight-year-old boy who is very mischievous always troubling his mother. His mother scolds him when he eats the toothpaste, urinate in bed at night. Naani falls down on a road one day and a young woman helps him. Naani's elder brother plans to watch adults movie with his friends in the absence of their parents and Naani demands him to join him to which his brother does not allow him. Angered, Naani cuts off the power which creates a short circuit at home. Naani's mother scolds for his dangerous mischief and shouts at her husband for not stopping with one child as Naani is troubling her a lot. This hurts Naani and he runs away from home to jump into a river. But he is stopped by an old man and he takes Naani to his place. The old man introduces himself as a scientist who has his own laboratory. He insists Naani to help him in his research of transforming a child to a young man. Naani agrees and the scientist transforms him to a young man. Naani starts to live as a young man physically but as a child mentally and stays away from his family. The only person other than scientist who knows the truth is his child classmate friend. Naani meets the girl at a park who helped him once he fell down on road. Innocent child Naani helps to remove dust from her eyes, smiles at her and leaves the place. The girl is very much attracted towards him and she looks for him every day.
Naani goes for an interview in a company under the name of Vichu. The company is toy manufacturing company and the owner who interviews him demands to have childhood memories and should be like a child to understand children's taste. Since Naani himself is a child he grabs the job easily. Vichu is diverted to the daughter of the owner who is none other than the girl named Priya who helped Naani once on road and whom she was helped by him at the park. Priya is surprised and happy to see him in her company. Priya-Vichu intimacy creates a jealousy for Raj another employee in the company who intends to attract her and marry her. The cold war continues when Naani overcomes Raj's idea for a new type of bed for kids and introduces his own idea creating a successful product. Naani meets his brother as an anonymous man and hears that his mother is very depressed on Naani's disappearance. Naani meets his mother who fell sick since her son got missed. She feels bad for having so strict to her child which she had done for his goodness. Naani realised his mother's love and goes to scientist to change him back to eight-year-old boy. Scientist understands his mind and he again transforms him to eight-year-old boy and Naani reconciles with his mother. But again at night he changes back to young man and he immediately rushes to scientist. But scientist does not know what has happened and both of them are shocked on Naani's present condition.
Naani now lives as an eight-year-old boy during day time and as a twenty eight-year man during night time. Priya expresses her love to him but Naani tells her to love a man suitable for her age. Scientist tells Naani to accept Priya and Vichu accepts her love. Priya tortures him always to which he cannot withstand. Priya tells him accompany for a matinee show. Since Naani is a boy during day time he cannot come. But he sees Priya waiting in anger for him in the theatre while going to home from his school along with his mother. Naani's mother befriends Priya as they are neighbours and Priya likes small boy Naani. Priya gets angry on Vichu's (Naani's) absence. She finally decides to both get married. Raj kidnaps Vichu on day of marriage but Vichu changes to Naani during daytime. The kidnappers release him as they misunderstand of kidnapping a child. Naani transforms to Vichu and marries Priya at evening time.(Hindu marriages take place usually at mornings). Vichu though a young man by body but small boy and does not know anything about marital life. Now Vichu lives as an eight-year son to his mother during days and as Vichu, an employee in his wife's company and as husband to his wife during night time. Naani somehow manages his mother by disappearing during nights.Priya needs a child so she intentionally shows her skin to him by intentionally removing her clothes. Priya is now pregnant and Vichu is now a child dad. Vichu once meets Naani's (his) mother and understands the difficulties of pregnancy for a woman. Hence he takes care of his wife with full affection. Naani's child friend demands to spend time and come to play with him but Naani refuses as has got tight schedule as a son, as an employee and as a husband. His friends get angry and reveals the truth to Priya. Priya is shocked to hear that she is bearing the child of a child.