// if self is a container controller and childController is a property of the container controller
// to add

[self addChildController: childController];
[self.view addSubview: childController.view];
[self.childController didMoveToParrentController: self];


// to remove

[self.childController willMoveToParrentViewController: nil];
[self.childController removeFromParrentVIewController];
if(self.childController.view.superView != nil)
    [self.childViewController.view removeFromSuperview];