Laravel5 event 'deleting' doesn't work on Model::whereIn()

I have one to many relation on user model, I have set a event when I delete user will dell all childs 'client'. on resource Controller destroy method event 'deleting' method is work for normally.

But I create a mass massDestroy method using Model::whereIn() 'deleting' event doesn't work.

Below is my relate code, How can I fix it?

UsersController relate code

public function destroy(User $user)
{
    $user->delete();

    return back();
}

public function massDestroy(MassDestroyUserRequest $request)
{
    if ($request->ajax()) {
        User::whereIn('id', $request->get('ids'))->delete();
    }

    return response(null, Response::HTTP_NO_CONTENT);
}

User Model relate code

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use SoftDeletes, Notifiable;

    public $table = 'users';

    //skip

    protected static function boot()
    {
        parent::boot();
        self::deleting(function (User $user) {
           $user->clients()->delete(); //doesn't work on Model::whereIn
        });
    }

    public function clients()
    {
        return $this->hasMany(Client::class, 'user_id', 'id');
    }
}

Client model relate code

public function user()
{
    return $this->belongsTo(User::class ,'user_id', 'id');
}

PS* I have try to delete one by one( very ugly code ) as below is normally work.

//UsersController

public function massDestroy(MassDestroyUserRequest $request)
{
    if ($request->ajax()) {
            $users = User::whereIn('id', $request->get('ids'))->get();
            foreach ($users as $user ) {
                $user ->delete();
            }
    }

    return response(null, Response::HTTP_NO_CONTENT);
}

via Chebli Mohamed