Horizontal padding between UIPageViewController child view controllers

check UIPageViewController init method

- (id)initWithTransitionStyle:(UIPageViewControllerTransitionStyle)style navigationOrientation:(UIPageViewControllerNavigationOrientation)navigationOrientation options:(NSDictionary *)opt

you can pass your inter page space value to opt in UIPageViewControllerOptionInterPageSpacingKey

With Swift, you can use initWithTransitionStyle:navigationOrientation:options: initializer and pass a value to UIPageViewControllerOptionInterPageSpacingKey in your options parameter to set a space between pages.

As an example, the following code shows how to implement it with Swift 2.2:

let optionsDict = [UIPageViewControllerOptionInterPageSpacingKey: 20]

let pageViewController = UIPageViewController(
    transitionStyle: .Scroll,
    navigationOrientation: .Horizontal,
    options: optionsDict
)

Note that the UIPageViewController class reference states about UIPageViewControllerOptionInterPageSpacingKey:

The value should be a CGFloat wrapped in an instance of NSNumber.

However, a Dictionary of type [String: Int], as shown in the previous code, also works.