A quick implementation of adding a child view controller to another view controller and specifies which view to add it to.

UIViewController+AddChild.m

@interface UIViewController (AddChild)

- (void)addChildController:(UIViewController*)childController toView:(UIView*)view;

@end

@implementation UIViewController (AddChild)

- (void)addChildController:(UIViewController*)childController toView:(UIView*)view {
    [childController willMoveToParentViewController:self];
    
    childController.view.frame = view.bounds;
    
    [view addSubview:childController.view];
    [self addChildViewController:childController];
    
    [childController didMoveToParentViewController:self];
}

@end