A Little Romance(1979)

Intellectually precocious teenager Lauren King lives in Paris with her somewhat ditzy mother. On a movie set, she strikes up a friendship with teenage film buff Daniel Michon. After Lauren's mother forbids her to date the outspoken Daniel, the young lovebirds team up with eccentric pickpocket Julius to run away to Venice, where, according to legend, a couple who kiss under the Bridge of Sighs will stay together forever.