C'est jeune et ça sait tout ! 1974

When Charles Le Braque learns that his boss' 17 years old daughter is pregnant, he fears that his 16 years old nice Joel from France, who's spending her vacation with them in Canada, might fall into the same trap. So he and his wife decide to give her the lecture of plants and bees... but it turns out that she's already well informed, gives them a lecture about simultaneous orgasms. She inspires the sexually repressed couple to start experimenting with "modern" forms of sex.