So ein Bienchen (1976)

Sabine, nicknamed Bienchen, was adopted when she was four. Now nine, she has a very good relationship with her 17-year-old adopted brother, Lutz, and spends a lot of time with him and his girlfriend, Anke. When Lutz and Anke go on an outing in Lutz’s grandfather’s motorboat, Bienchen, the neighborhood boy Lampe, and his little brother Spinne are determined to come along too. There is tension between Lutz and Anke because Anke is very sensible, while Lutz often ignores the rules: he speeds in the boat and gets caught by his father, who works for the water police. At a garden café, he drinks several beers, and despite his father’s and Anke’s warnings to leave the boat and take the bus back, he takes the boat. He has had enough of Anke’s sensible ways and goes to the youth club without her the next day, where he meets another girl: Kerstin, the singer in the band performing at the club that evening. Before long, he takes Kerstin out in the boat and breaks up with Anke. Bienchen is angry with her brother: she likes Anke a lot and had hoped the two of them would get married. Inspired by Max and Moritz, she and Lampe decide to play a trick on Lutz and rig his cigarettes with cap gun caps, so they explode when he smokes them. Later, Lutz wants to make up with his little sister and take her on a boat trip with Kerstin. Bienchen reluctantly agrees, then uses the outing to play more tricks on Kerstin and Lutz. That evening, Lutz brings Kerstin home for the first time, and Kerstin has a chance to tell their parents about Bienchen’s pranks—but she doesn’t, and Bienchen is reconciled with her. After dinner, Kerstin wants to play the piano for the family—but Lampe has rigged the piano hammers with cap gun caps too. Lutz believes Bienchen when she says she knew nothing about it, preventing another argument between the siblings.