Vice Versa (movie, 1948)

Businessman Paul Bultitude is sending his son Dick to a boarding school. While holding a magic stone from India, he wishes that he could be young again. His wish is immediately fulfilled and the two change bodies with each other. Mr Bultitude becomes a school boy who smokes cigars and has a very conservative view on child upbringing, while his son Dick becomes a gentleman who spends his time drinking lemonade and arranging children's parties.