Many people in the Rust community use some sort of ECS in cases where something like a GC is needed. The whole point of ECS is that they work a lot like an ordinary GC runtime or an in-memory database, the underlying representation ensures that the system knows about all the "entities" that it needs to, and can reliably trace linkages between them. It might be easier to just use Go in cases where tracing GC is needed, though.

In a language with tracing GC, you'd use a strong reference in both directions, so anybody who holds the child can always walk their way to the root (if you expose those references). Without such GC, you basically have to pass the root around, because it's what's holding all those children alive.

What's not solved with manual memory management? The point is not that you can't solve it, the point is that reference counting isn't the whole solution for garbage collection unlike a tracing gc for instance.

It can always be solved with weak references.