IT Chapter Two had to get creative to bring the young cast back, and they used quite a few tricks to do so. Even though they were the stars of the first film, IT Chapter Two continues the story 27 years later. This results in the adult versions of the Losers' Club taking on the leading roles in the sequel. But, the younger cast of Finn Wolfhard (Richie), Sophia Lillis (Bev), Jack Dylan Grazer (Eddie), Jaeden Martell (Bill), Jeremy Ray Taylor (Ben), Chosen Jacobs (Mike), and Wyatt Oleff (Stanley) from 2017's IT do return to take on Pennywise.
This was inevitable after the enormous success of the movie at the box office, and Stephen King's novel served as a guide to make their returns possible. The events of the book are told concurrently through the eyes of the kids and their adult selves. While this narrative choice wasn't used for IT, the sequel dabbles with this idea by flashing back to the summer of 1989. However, this was more difficult to do than some may think thanks to a two-year gap between productions allowing plenty of time for the kids to mature. Their changed appearances meant that IT Chapter Two had to use some tricks to make them return to their looks from IT.
As discussed in a new video from Screen Rant, one of the tricks that IT Chapter Two had to use across the board was de-aging technology. This process has become increasingly common in Hollywood, and the horror sequel used it to make the young actors look like they did two years ago. The process was simple for the actors, requiring them to do a scan of their face and then left the de-aging process to VFX teams. The results are noticeable, especially if you're aware that it happened, as they don't all look quite the same as they did before. Wolfhard's younger Richie, specifically, looks slightly off. Maybe more of the IT Chapter Two's budget should've gone in this direction.
In addition to aging them down, the team behind IT Chapter Two also had to figure out how to make the kids' voices match their younger selves. Since they all grew up and matured through puberty between shoots, many of the boys had deeper voices when it came time for the sequel to film. Hiring other voice actors to replicate their higher-pitched voices was considered by the studio but was not the path they went down. Instead, the kids were asked to try and duplicate their younger high pitched voices naturally.
A noticeable physical transformation that hit the young stars was also growth spurts. For anyone who has watched Stranger Things, it is clear just how much taller Wolfhard is now than he was a few years ago. He wasn't the only one though, as Taylor also was nine inches taller by the time IT Chapter Two began. These growth spurts had to be addressed during production. They didn't manipulate them digitally after the fact though and instead decided to cleverly frame the actors so that their heights matched.
Through these three behind-the-scenes tricks, IT Chapter Two was able to bring the young cast back with the same look and sound that audiences remembered from the first film. It just goes to show how quickly kids grow up and the lengths that studios have to go through sometimes to for the desired outcome. If they planned ahead, all of this could've been avoided by filming these scenes during principal photography of the first movie. But, at least IT Chapter Two still managed to pull this off somehow.