Le petit amour (1988)
Directed by Agnès Varda. With Jane Birkin, Mathieu Demy, Charlotte Gainsbourg, Lou Doillon. Mary-Jane asks, "Do all women fall in love with a boy, or just those without sons?" She's divorced with two daughters, Lucy and Loulou. Lucy has a party where Mary-Jane notices Julien, 14, small and brassy, but she sees a sensitive side.
http://www.imdb.com/title/tt0093371/