James Cameron recently told Entertainment Weekly that part of the reason he decided to film “Avatar: The Way of Water,” “Avatar 3” and some of “Avatar 4” all at once is because he wanted his franchise to avoid what he called “the ‘Stranger Things’ effect,” or when child actors grow up so fast in between installments that eventually they stop resembling children.
Source: James Cameron: Avatar 2 Kids Had to Avoid Stranger Things Aging – Variety