The Marvel Cinematic Universe introduced audiences to Scott Lang and his daughter, Cassie Lang, in 2015's Ant-Man. Abby Ryder Fortson was the original Cassie Lang, being eight years old in the film. By the time of 2019's Avengers: Endgame, which followed a five-year gap in the MCU timeline, Cassie was played by Emma Fuhrmann as a teenager. However, Cassie Lang was recast yet again for Ant-Man and the Wasp: Quantumania.
Source：https://www.cbr.com/ant-man-why-cassie-lang-recast-mcu/
