Eight-year-old Marco Marinelli is a bedwetter, scolded by his mother (Ottavia Piccolo) and teased by his classmates. On his birthday he finds out that his father (Alessandro Haber), who is facing economic difficulties, hasn't brought him the Lego he was promised. He runs in tears to his room and puts all his heart into wishing he were big and not subject to these indignities. As a result, he bursts through his clothes in the guise of a forty-year-old man (Renato Pozzetto) and seeks refuge in the house of his schoolteacher Francesca (Giulia Boschi), who he's secretly in love with. Mentally, he is still eight years old, and it's a puzzle what to do with him, until someone discovers that he has an uncanny rapport with children. Then he becomes a full-time and highly requested babysitter, but shortly after he is suspected of abducting the by-now long-missing child Marco. He then runs out of money, and fakes the kidnapping of himself, but while chased by the police he eventually turns back into the eight-year-old boy. He leaves a letter to Francesca who, upon realising the boy and man were one, uses the magic to join him as a little girl.