In the Haskell world, folks have solutions to both of these problems:
The "large-object problem" can be tackled in a principled fashion using strict state threads (aka the ST monad: https://wiki.haskell.org/Monad/ST) or using vanilla mutable (IORef) references.
The "parent-child problem" is well-addressed by lenses, also known as functional references. They are basically composable getters and setters that allow you to read or update deep into nested structures.
The "large-object problem" can be tackled in a principled fashion using strict state threads (aka the ST monad: https://wiki.haskell.org/Monad/ST) or using vanilla mutable (IORef) references.
The "parent-child problem" is well-addressed by lenses, also known as functional references. They are basically composable getters and setters that allow you to read or update deep into nested structures.