Default sub-pages on WordPress Multisite

wp_insert_post() returns a post ID for the fresh post. You can use that ID to set a parent post.

Example

$about_id = wp_insert_post(
    array (
        'post_title'   => 'About',
        'post_status'  => 'publish',
        'post_type'    => 'page',
    )
);
wp_insert_post(
    array (
        'post_title'   => 'Information',
        'post_status'  => 'publish',
        'post_type'    => 'page',
        'post_parent'  => $about_id,
    )
);

In your case, I would restructure the page data and build a nested array:

$default_pages = array(
    'Contact'     => array(
        "content" => "This is your 'Contact' page. Enter in your content here."
    ),
    'About'       => array(
        "content" => "This is your 'About' page. Enter in your content here.",
        "children" => array(
            'Information' => array(
                "content" => "This is your 'Information' page. Enter in your content here."
            )
        ),
    ),
    'Home'        => array(
        "content" => "This is your 'Home' page. Enter in your content here."
    ),
);

Then I would move the page insertion to a separate function to allow recursion:

function insert_page( $title, Array $properties, $post_parent = 0 )
{
    $data = array(
        'post_title'   => $title,
        'post_content' => $properties[ "content" ],
        'post_status'  => 'publish',
        'post_type'    => 'page',
        'post_parent'  => $post_parent,
    );

    $id = wp_insert_post( add_magic_quotes( $data ) );

    if ( ! empty ( $properties[ "children" ] ) )
    {
        foreach ( $properties[ "children" ] as $child_title => $child_properties )
            insert_page( $child_title, $child_properties, $id );
    }
}

So your complete code should look like this:

function default_pages( $blog_id )
{
    $default_pages = array(
        'Contact'     => array(
            "content" => "This is your 'Contact' page. Enter in your content here."
        ),
        'About'       => array(
            "content" => "This is your 'About' page. Enter in your content here.",
            "children" => array(
                'Information' => array(
                    "content" => "This is your 'Information' page. Enter in your content here."
                )
            ),
        ),
        'Home'        => array(
            "content" => "This is your 'Home' page. Enter in your content here."
        ),
    );

    switch_to_blog( $blog_id );

    if ( $current_pages = get_pages() )
        $default_pages = array_diff( $default_pages, wp_list_pluck( $current_pages, 'post_title' ) );

    foreach ( $default_pages as $page_title => $properties )
        insert_page( $page_title, $properties );

    restore_current_blog();
}

function insert_page( $title, Array $properties, $post_parent = 0 )
{
    $data = array(
        'post_title'   => $title,
        'post_content' => $properties[ "content" ],
        'post_status'  => 'publish',
        'post_type'    => 'page',
        'post_parent'  => $post_parent,
    );

    $id = wp_insert_post( add_magic_quotes( $data ) );

    if ( ! empty ( $properties[ "children" ] ) )
    {
        foreach ( $properties[ "children" ] as $child_title => $child_properties )
            insert_page( $child_title, $child_properties, $id );
    }
}