A ViewController in iOS is just an object that is bound to a view. A viewcontroller in interface builder can have a million view controllers as properties, although theres not reason for that unless the view that is connected to the view controller has a million subviews and they all need their own controller.
You can NOT state that there is view controller containment in iOS. That makes no sense.
Please understand that a view controller contains nothing but a view and any outlets or code that you add to it.
It can load and show another view controller. It can hold a reference to another view controller.
But view controllers do not through any hierarchical means contain another view controller.