Director Andy Muschietti revealed to Total Film magazine early on they “knew that [de-ageing] would be part of the budget” due to a number of flashback scenes.
He added that Finn “grew up quite a bit” between the two films which were shot two years apart.
“It’s better to shoot it two years later than five years later,” he said. “But in those two years, they grew up quite a bit. Not all of them. Sophia [Lillis] looks exactly the same. Jaeden [Martell] looks pretty much the same.”
“Finn grew up quite a bit, and he’s a tall guy. But from the beginning, we knew that that would be part of the budget, the visual effects to address that. So we’re going to de-age the kids.”
This is what Finn looked like in the first It movie:
And this is what he looks like now:
Look at how tall he is!
Anyway, in case you missed the most recent It: Chapter Two trailer, here’s what Finn looks like after being digitally de-aged:
He actually looks adorable and not that far off how he looked in the first film which is pretty amazing. Those glasses and his huge eyes definitely make it look like a Snapchat filter was used though.
In this shot taken on set you can see how much older he looked while filming:
It’s unclear just yet on whether Jack Dylan Grazer or Chosen Jacobs were de-aged.