Create models when creating parent (E.g. creating 5 posts when a user is created)

If a User has many posts, and a post belongs to user, it's simple to do:

$factory->define(App\Post::class, function ($faker) {
    return [
        'title' => $faker->title,
        'content' => $faker->paragraph,
        'user_id' => function () {

            // Creates a User for every Post
            return factory(App\User::class)->create()->id;
        }
    ];
});

How do I accomplish the opposite? Instead, creating say 5 posts when a user is created and associating that post to the newly created user?

via Chebli Mohamed