The National Lampoon’s Vacation series is one of the most popular family franchises of all time, but it suffers from an important continuity error involving the actors, ages, and appearances of the Griswold children. The Vacation film series follows the Griswold family of Clark and Ellen and their two children Rusty and Audrey. Over a series of four original films, the Vacation movies depict the Griswolds’ misadventures surrounding vacations and holidays as Clark strenuously attempts to make the most out of every experience. While the Griswold family is at the center of each movie, the actors are not always the same.

https://screenrant.com/national-lampoons-vacation-griswold-rusty-audrey-change-why/