The Child Crank Option is made to be used with children between 5-10 years old who are unable to reach the pedals with the rear saddle fully lowered. The installation instructions are included in the box. When installing this kit on a tandem, make sure that its rear seat tube is 1 3/8" (35mm) in diameter and it is equipped with crossover drive (chain on left side of bicycle connecting captain to stoker crank). In order to use the 38 tooth chainring that is supplied, the rear crossover arm must have the 110 mm bolt circle with five arms.