Child TNObjects have IDs of their parent and all communication goes through the parent. I actually expanded on this in the latest version of TNet on my end (not yet public), but it's still the same.
You can instantiate two objects then set one to be parented to another at run time yourself, just be aware that destroying the root object will end up destroying the local copy of the child, without actually removing it from the server -- likely leading to errors.
It's often better to just set one object to copy the transform of another in Update() or LateUpdate().