そうして、マイグレーションを修正するには、「child.php」→「Child.php」に変えました

backend/app/Models/FatherRelations.php

@@ -1,14 +0,0 @@
-<?php
-
-namespace App\Models;
-
-use Illuminate\Database\Eloquent\Factories\HasFactory;
-use Illuminate\Database\Eloquent\Model;
-
-class FatherRelations extends Model
-{
-    public function father ()
-    {
-        return $this->belongsTo(Fathers::class);
-    }
-}

backend/app/Models/Fathers.php

@@ -1,14 +0,0 @@
-<?php
-
-namespace App\Models;
-
-use Illuminate\Database\Eloquent\Factories\HasFactory;
-use Illuminate\Database\Eloquent\Model;
-
-class Fathers extends Model
-{
-    public function relations ()
-    {
-        return $this->hasMany(FatherRelations::class);
-    }
-}

backend/database/migrations/2021_09_28_051525_create_fathers_table.php

@@ -1,33 +0,0 @@
-<?php
-
-use Illuminate\Database\Migrations\Migration;
-use Illuminate\Database\Schema\Blueprint;
-use Illuminate\Support\Facades\Schema;
-
-class CreateFathersTable extends Migration
-{
-    /**
-     * Run the migrations.
-     *
-     * @return void
-     */
-    public function up()
-    {
-        Schema::create('fathers', function (Blueprint $table) {
-            $table->id();
-            $table->integer('company');
-            $table->string('image');
-            $table->timestamps();
-        });
-    }
-
-    /**
-     * Reverse the migrations.
-     *
-     * @return void
-     */
-    public function down()
-    {
-        Schema::dropIfExists('fathers');
-    }
-}

backend/database/migrations/2021_09_28_051537_create_father_relations_table.php

@@ -1,32 +0,0 @@
-<?php
-
-use Illuminate\Database\Migrations\Migration;
-use Illuminate\Database\Schema\Blueprint;
-use Illuminate\Support\Facades\Schema;
-
-class CreateFatherRelationsTable extends Migration
-{
-    /**
-     * Run the migrations.
-     *
-     * @return void
-     */
-    public function up()
-    {
-        Schema::create('father_relations', function (Blueprint $table) {
-            $table->id();
-            $table->integer('father_id');
-            $table->timestamps();
-        });
-    }
-
-    /**
-     * Reverse the migrations.
-     *
-     * @return void
-     */
-    public function down()
-    {
-        Schema::dropIfExists('father_relations');
-    }
-}

backend/database/seeders/FatherRelationsSeeder.php

@@ -1,21 +0,0 @@
-<?php
-
-namespace Database\Seeders;
-
-use Illuminate\Database\Seeder;
-use Illuminate\Support\Facades\DB;
-
-class FatherRelationsSeeder extends Seeder
-{
-    /**
-     * Run the database seeds.
-     *
-     * @return void
-     */
-    public function run()
-    {
-        DB::table('father_relations')->insert([
-            'father_id' => 1,
-        ]);
-    }
-}

backend/database/seeders/FathersSeeder.php

@@ -1,22 +0,0 @@
-<?php
-
-namespace Database\Seeders;
-
-use Illuminate\Database\Seeder;
-use Illuminate\Support\Facades\DB;
-
-class FathersSeeder extends Seeder
-{
-    /**
-     * Run the database seeds.
-     *
-     * @return void
-     */
-    public function run()
-    {
-        DB::table('fathers')->insert([
-            'company' => 1,
-            'image' => '',
-        ]);
-    }
-}